* turned all attributes of the "Blockdevice" class into properties (postponing evaluation)
* unify cache_links for blockdevice information
* add default location of config file to preferences handling
* try to refresh the block device cache once if a device was requested, that is currently not in the list (after a minimum cache age passed)
* added an implicit sorting function for block devices (based on major/minor values)
* try all found device nodes, in case the first does not exist anymore (e.g. temporary device nodes)
* significantly reduced the time required for generating the block device list:
* use a cache for major/minor -> device nodes mapping
* run 'blkid' only once for LABEL, TYPE and UUID
* added some code for (optional) profiling via python-profiler
replaced some functions in container.py with their new blockdevice.py counterparts
move "type_id" detection from container.py to blockdevice.py
reduce calls of "reset" for blockdevices
added UUID detection for blockdevices
changed interface of cryptobox.core.container and cryptobox.core.main for new blockdevice detection
* beware: the change is not finished - the cryptobox is not working properly for now
added allowedProg "pvdisplay" to CryptoBoxRootActions to allow LVM detection
improved blockdevice handling: caching and detection of lvm, luks and raid