The following directory structure is required:
	- python code: plugins/PLUGINNAME/PLUGINNAME.py (all lower case is recommended)
	- language file: plugins/PLUGINNAME/language.hdf
	- clearsilver templates: plugins/PLUGINNAME/*.cs
	- icon (128x128px recommended): plugins/PLUGINNAME/plugin_icon.png
	- css stylesheets (optional): plugins/PLUGINNAME/PLUGINNAME.css


Python code interface:
	- create a class with the same name as the plugin - it must inherit CryptoBoxPlugin
	- function "do_action":
		- this function will get called whenever this plugins is involved in a request
		- all arguments should be optional (e.g. for displaying a form without previous input values)
		- the argument "store" should be used to process a form submission (just a recommendation)
		- if the processing failed for some reason (invalid input, ...), it should manually set
		  "Data.Warning" or "Data.Success") to a value of your choice (preferably
		  you may want to use messages of the namespace of your plugin
		  (e.g. "Data.Plugins.PLUGINNAME.WarningMessage.InvalidInput"))
		- the return value should be the name of the template that should be displayed after processing
		  (a template file in the plugin directory takes precedence over global template files)
			- the return value may also be a dictionary with the following elements:
				* template: the name of the template file (mandatory)
				* generator: a generator object ("yield") - its content will replace every
				  occurrence of "<!-- CONTENT_DUMMY -->" in the template (useful for pages that
				  are displayed step by step (as for formatting of filesystems))
			- the return value may also be a dictionary with the following elements:
				* plugin: the name of a plugin
				* values: a dictionary of variables that should be defined for this plugin
			- an empty (e.g. None) return value can be used to go to the default page ("disks"
			  or "volume_mount" (for volume plugins))
	- function "get_status":
		- returns a string, that describes a state connected to this plugin (e.g. the current date and
		  time (for the "date" plugin))
	- function "handle_event(event, event_info)":
		- may be overridden to specify event handling (e.g. "bootup", "shutdown")
		- see src/cryptobox/plugins/base.py for details
	- the class variable "plugin_capabilities" must be an array of strings (supported: "system" and
	  "volume")
	- the class variable "plugin_visibility" may contain one or more of the following items:
	  menu/preferences/volume. This should fit to the 'plugin_capabilities' variable.
	  An empty list is interpreted as an invisible plugin.
	- the class variable "request_auth" is boolean and defines, if admin authentication is necessary
	  for this plugin
	- the class variable "rank" is an integer in the range of 0..100 - it determines the order
	  of plugins in listings (lower value -> higher priority)
	- volume plugins contain the attribute "device" (you may trust this value - a volume plugin will
	  never get called with an invalid device)
	- the python module which contains the plugin's class should also contain a class called
	  'unittests' - it should inherit WebInterfaceTestClass.WebInterfaceTestClass


Language file structure:
	- the content of the language file will be added to the hdf dataset below "Lang.Plugins.PLUGINNAME"
	  (this avoids namespace conflicts)
	- the following top level settings _must_ be defined:
		Name (a short description)
		Link (the visible text for links to this plugin)
	- all warnings, hints and success messages should be stored below WarningMessage.???
	  (resp. AdviceMessage or SuccessMessage)


Clearsilver template:
	- heading:
		- non-volume plugins: "<h1>" 
		- volume plugins: "<?cs var:plugin_heading ?>" (very important - otherwise
		  embedding of plugins breaks (see 'volume_properties'))
	- the title should be followd by '<?cs call:handle_messages() ?>'
	- usually you should supply some helpful information afterwards (only displayed
	  if the user enabled inline-help before):
	  	"<?cs call:show_help(Lang.Plugins.PLUGINNAME.Help.Text) ?>"
	- links to the plugin (e.g. in form headers) could look like the following:
		<?cs call:link("PLUGINNAME",'','','','') ?>