Add initial .desktop file and icon copied from the launcher source
tree, and updated .pro files to install them. Also removed potentially
confusing use of non-existent $$PREFIX variable.
Bug-AGL: SPEC-4182
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: I5b6a0fee2b02e4e5132689b8d892ce5f8480cc42