Support UI Thread Separate (UTS) App Model (#464)

Support UI Thread Separate (UTS) App Model (#464)

define new apptype dotnet-uts for UI Thread Separate App Model

In the UI Thread Separate App Model, the main thread operates with the gmainloop
and UI-related tasks operate with the ecoreloop in a separate thread.
Therefore, ecore_init() should not be called in the main thread of the candidate process
for the UI Thread Separate App Model.
Also, candidate process should run with the gmainloop.

To run by the UI Thread Separate App Model, the environment variable "TIZEN_UI_THREAD" should be set to "true".
If this environment variable is set, then NUI would work on UI Thread Separate Mode.