Don't remove from container if container is empty
Select "General" tab by default in options window
Remember last saved GIF directory + fix overwriting existing GIF

- Remembers the directory where the last GIF was saved
- Fixes a bug where overwriting an existing GIF did not succeed
due to QFile::copy not overwriting existing files
Disable FFVideoSource cache file (.ffindex)
Pause frame generator when asking to quit the app
Refactor pausing and resuming frame generator in its own member functions
Add open recent menu
Move thumbnail resizing into videoframethumbnail constructor
Remove missing item from recent menu when clicked

If an item from the recent menu is not found when clicked remove the item
and rebuild the recent menu
Add override
Add doxygen comments to recent menu member functions
Add const to exception catch statements