Change MCSystemPlaySound to take a StringRef

Both iOS and Android platforms changed.
Change MCSystemPlayVideo to take a StringRef

Both Android and iOS platforms have been modified.
Updated MCSystemGetPlayingSound to return a StringRef

The s_sound_file global variable is now assigned an empty string when no sound is playing rather than being nil.
Restore accidentally removed behaviour in MCMultimediaEvalSound

The pre-refactor behaviour was to return the string "done" when no sound is playing; this was accidentally removed.
Update MCSystemSound{Player,Channel} to use StringRef names

The class MCSoundFinishedOnChannelEvent and the function MCSoundPostSoundFinishedOnChannelMessage have also been updated.

Both Android and iOS have been changed.
Update MCNotificationPost* functions to take StringRefs

The m_device_token and m_launch_url members of @interface MCIPhoneApplication were changed to StringRefs as was m_notification of MCNotificationEvent.
Convert MCMiniZip to use StringRefs
Revert edits to cmdse.cpp and funcs.cpp

Accidental edits made to code within an #ifdef LEGACY_EXEC block.
Use MCStringBeginsWithCString where appropriate

Replaced calls to MCStringBeginsWith using a C string with calls to the more appropriate function.
Fix an incorrect function signature

The extern declaration for MCSystemGetPlayingSound in MCMultimediaEvalSound had the wrong signature.
Minor fixes

Tidy up a JNI function by using MCJavaStringToStringRef and remove an un-neccessary check for empty names.
Add MCSystemSound{Initialize,Finalize} functions

Both Android and iOS now call these functions at startup/shutdown.
Fix silly mistakes

Fixed a couple of silly mistakes where the return value wasn't being set.
Updates on MCObject::domess() method
Updated eval(), FindFileIndex(), FindFile() and Include() methods
Reverted submodule changes
Updates after feedback #1
The external loading interface now takes StringRefs
Fix some Android-specific external loading code
Remove MCDispatch::isolatedsend

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