plugin plugin_manager: prevent browser from caching repeatitive actions
plugin plugin_manager: add support for properties/volume visibility
plugins: moved message handling to central header file (templates/header.cs)
splitted 'volume_props' into 'volume_rename' and 'volume_chpasswd'
volume_props: turned into a container for small property changes
renamed 'format_fs' to 'volume_format_fs'
moved inclusion of 'show_volume_[header|footer].cs' to central header file