Fix BGM adjustment in cutscenes not blocking

BGM.isAdjusting() was always returning false due to a regression caused
in the earlier conversion from Tween.js to Scenario.  This prevented the
adjustBGMVolume scenelet from blocking--which would have thrown
cutscenes out of sync.
Re-render 'Bruce Tells His Story' BGM

New track rendered in foobar2000 with the foo_midi plugin in BASSMIDI
mode, using the Chorium soundfont, at 48 kHz.  Sounds much better than
the old 22 kHz render in adlmidi mode!
Allow hiding speaker in textboxes

The opening narration isn't nearly as effective emotionally when Bruce's
name is displayed constantly, but simply passing null for a speaker
causes the full width of the textbox to be used for dialogue, which
hurts it aesthetically.  So now the talk scenelet takes an additional
argument, 'showSpeaker', which if set to false, hides the speaker's name
but aligns the text as if the name were visible.
Create test map and spriteset as placeholders

Should make prototyping cutscenes and such a bit less painful if I have
a designated test map I can use as placeholder...