Clean up

Added deinit's for lbrace and rbrace.
Removed all 'introduction'-related code.
Removed old commented-out animation code.

Keeping bg_default's BmpContainer's definition and deinit. For some
reason, removing them causes the app to crash. Requires further
investigation.
bool bracesOpen

Added bracesOpen:
- Set visibility of time and brace_hider_layer accordingly
- Allow animations accordingly
Braces are hidden at initialization.
update_watchface and timer_handle no longer called at initialization.
set_container_image called on intialization to place the default arch
image.

TODO: test setting bracesOpen with an animation-ended callback