Add also a GUI (window) notification when cannot start a VM due to some error

[joanna]

... e.g. due to insufficient memory error. Currently it is only displayed to the user when the user uses a command line tool to start a VM:

[joanna@dom0 ~]$ qvm-start personal-win7
--> Loading the VM (type = HVM)...
Traceback (most recent call last):
  File "/usr/bin/qvm-start", line 93, in <module>
    main()
  File "/usr/bin/qvm-start", line 88, in main
    xid = vm.start(debug_console=options.debug_console, verbose=options.verbose, preparing_dvm=options.preparing_dvm)
  File "/usr/lib64/python2.6/site-packages/qubes/qubes.py", line 1368, in start
    raise MemoryError ("ERROR: insufficient memory to start this VM")
MemoryError: ERROR: insufficient memory to start this VM

When starting via appmenus (and probably also via manager) NOTHING is displayed!

[marmarek]

​http://git.qubes-os.org/gitweb/?p=marmarek/core.git;a=commit;h=9927244670ef809d4f9873c1ccb73f24107c5a00