EMI: Rework text stack handling

The text stack in EMI must be saved and restored in save games because
the game will call PopText after returning from the menu. Instead of
managing separate lists for each text stack level this patch adds a
_stackLevel field that is incremented for PushText and decremented for
PopText. Only text objects from the stack top (level 0) are rendered.
Merge pull request #773 from inguin/emi-text-stack

EMI: Rework text stack handling
Merge pull request #766 from chkr-private/sound-fixes

EMI: Music and sound effect enhancements
EMI: Patch a typo in mot.lua

This caused issues with guybrush using his inventory while on the raft
EMI: fix attached actor handling in swamp

Time paradox is now playable.

- local _pos and _yaw values seem to be relative
to the actor where the current actor is attached to

- to accomodate this, Lua_V1::GetVisibleThings,
Actor::getYawTo and Actor::getSimplePuckVector should use
world coordinates