Make OSX test application compatible with current 10.10 beta SDK

The NSApplication delegate was changed from a setDelegate/delegate
method pair to a property, while the definition of NSApp didn't change
(its type is id while the type should be NSApplication* or similar)

Fixes jp9000/obs-studio#221
V4L2: Fix 'show_cursor' setting forcing default
window capture:  Fix defaults overriding values
Fix function typo (obs_data_get_autoselect_bool)
Add .desktop file for obs on linux
Install desktop file and application icon on linux