New GTK API fm_launch_command_simple()

It implements "do something with file(s)" sort of work.
Option "Format volume" for Places view volume items.

Also added option 'format_cmd' into config file.
It is visible only for unmounted local volumes and only if 'format_cmd' is defined.
Single column in RTL Compact view mode should be aligned to right border.

Usually columns are aligned to left but in RTL it should be not. Fixed.