Update MCSystemPick to take a StringRef

Updated for both Android and iOS (not used on desktop; Android is a nop)
Add MCNAME: an equivalent of MCSTR for NameRefs

Does exactly what it says on the tin.
Stack loading code now uses StringRefs/NameRefs
Replaced MCmessagenamestring with MCN_messagename
Add ConvertToBinary to MCExecContext

For ValueRefs that aren't already a DataRef, this converts to a string and then creates a DataRef out of the native bytes of the string.
Change MCU_puturl to use an ExecContext instead of an ExecPoint

An overload still taking the traditional EP has been provided for existing callers.
Change MCNetworkExecPutIntoUrl to no longer use GetEP

Does its thing using an ExecContext instead of an EP now.
Merge branch 'refactor-syntax_unicode' into refactor-syntax_unicode_findstack

Conflicts:
	engine/src/dispatch.cpp
Merge branch 'refactor-syntax_unicode_button_menu' into refactor-syntax_unicode_mcsystempick

Conflicts:
	engine/src/button.cpp
	engine/src/mbliphonepick.mm
Remove most uses of EPs from MCObject::eval
Fix errors and oversights
Yet more (attempted) fixes
More corrections
Fix a potential assertion failure
Replace an incorrect check for an empty string
Merge branch 'refactor-syntax_unicode' into refactor-syntax_unicode_findstack

Conflicts:
	engine/src/stack.h
MCEmbeddedPostEvent::Dispatch() updated
Merge branch 'refactor-syntax_unicode' into refactor-syntax_unicode_embedded_dispatch
Merge branch 'refactor-syntax_unicode' into refactor-syntax_unicode_embedded_dispatch
NSString creation updated to stringWithMCStringRef