#change Added (desktop) platform abstraction for checking if UBT is running. Fully functional for Windows, WIP for Mac and Linux (should work, but can give false positives)
[CL 2302894 by Robert Manuszewski in Main branch]
Fixed CONSTEXPR definitions.
Converted EFontImportFlags to an enum class in order to test this feature.
#codereview robert.manuszewski,john.barrett
[CL 2254804 by Steve Robb in Main branch]
refactored tga code to allows use outside of EditorFactories.cpp
added support for grayscale jpeg
fix memory leak in jpeg code
changes in AssetTools to allow to specify precise factory when multiple factories support the same filetype
changes in Plugin.cs to allow binary only plugins
exposed parts of engine API to other modules
[CL 2108453 by Matt Kuhlenschmidt in Main branch]
Whenever a blank engine association is read from a .uproject via GetEngineIdentifierForProject(), it checks up the directory hierarchy for an engine capable of loading it via its .uprojectdirs search directories. If found, it will use that engine's local identifier from the registry, or register it if it doesn't exist.
Setting a project's engine association to an engine which is capable of loading it via it's .uprojectdirs will cause it to write a blank engine association string into the .uproject (and triggering the behaviour above on open).
#codereview Michael.Trepka
[CL 2064463 by Ben Marsh in Main branch]
* Lots of code moved into IDesktopPlatform for sharing with Launcher and Mac (including setting up file associations, querying project versions, etc...)
* Hack to enumerate all the known launcher engine installations. Does not use registry keys any more. Will probably change to use a list of installations generated by the launcher at some point soon.
* List of registered GitHub builds is stored in HKEY_CURRENT_USER
* Switching engine versions is now done through a dialog rather than through the context menu.
* VersionSelector includes a version number for shell integration, allowing it to defer to an existing installation of the same version if necessary.
#codereview Michael.Trepka
[CL 2045845 by Ben Marsh in Main branch]
