Merge pull request #1313 from rlofc/next

Added GTK-based displayFileDialog implementation for Linux
Makes GTK non-optional for PlatformLinux displayFileDialog.
Removes unused Social defs.
Merge pull request #1314 from seanpaultaylor/next

Makes GTK non-optional for PlatformLinux displayFileDialog.
Minor cleanup on CMakeLists.txt and PlatformLinux.cpp
Merge pull request #1315 from seanpaultaylor/next

Minor cleanup on CMakeLists.txt and PlatformLinux.cpp
Fix #1000. Fire NOT_COLLIDING on removal if colliding.
Merge pull request #1316 from kwhatmough/next

Fix #1000. Fire NOT_COLLIDING on removal if colliding.
Fixed cursor disappearing when using setCursorVisible in Linux