load behaviors from score

[matthewdean]

A few comments:

• The Director engine treats sprites and frame scripts similarly (e.g. beginSprite and endSprite are called for both, see https://dreamlight.com/insights/07/behavior.htm#02-20-02 for details) so I've opted to unify their treatment. This required changing channels to be indexed starting at 0, as I've seen instances where frame scripts use channel 0.
• The code which loads sprites from score (Score::load_from_dir) is likely Director version dependent and I've only written it to account for Director 7 - will need to modify it to check version

[matthewdean]

From @igorlira on a previous version of this pull request:

I've noticed that we're only loading sprite data for the first frame (according to the log), plus the sprites seem to be loading into the wrong channel in dirplayer, I wonder if that has anything to do with it

Refactored sprite initialization so it happens every frame. Also am now adjusting the frame index as deserialized from the score to make it a correct channel number.

Have a number of other smaller changes sprinkled into this branch - mostly implementing unimplemented functions - if necessary can recreate them on other branches and submit them as separate pull requests.