better start menu integration: provide tools, on-off via magic key, start if needed

[Antoine Martin]

The new feature in 0.11.3 to wrap regular commands via winswitch_command_wrapper is very neat (and fast too!), but for more people to use it we need to make it easier to setup: provide a tool to make it easier to convert a bunch of .desktop files to use/not-use the wrapper.

It needs to:

• be able to run as root to change system wide settings
• run as user and save to user specific shortcuts
• take the blacklists into account so we don't convert software that does not work (see #132)

The ​freedesktop menu specification seems to allow this sort of thing. ​The freedesktop menu article covers similar grounds to what we want (refers to the 'alacarte' menu editor and covers the drawbacks of duplicating menu entries)

The wrapper also needs an easy way of being toggled:

• global on/off option which can be changed from applet
• detect magic key and based on wrapper_magic_key_action, either:
  • launch via wrapper
  • do not launch via wrapper (if default is off)
  • ask
• option to start the applet if it is not running

Also maybe:

• detect if the desktop files have been modified (ie: by OS upgrades) and re-apply the changes