MindTouchDream.sln: remove 'Mixed Platform' and 'x86' build targets
XUri:
* removed XURI_USE_NAMETABLE conditional build variable
* made XUri serializable again (though we really don't like it)
Merge branch 'UriParseOptimize' into DR-117

Conflicts:
	src/MindTouchDream.sln
	src/mindtouch.dream/dream/XUri.cs