Improve pixel API

[henrygab]

Current RGB API does not play well with others (animation from config file overwrites any other use of the pixels).

The improved API should aim to do the following:

1. Safely avoid touching hardware when pixel subsystem is not initialized or otherwise disabled
2. Allow "reserving" bitmask of individual pixels (w/ uint32_t owner tag or similar for debugging)
3. Allow "releasing" bitmask of reserved pixels (w/ uint32_t owner tag or similar for debugging)
4. Automatically pause any configured animation when at least one pixel is reserved
5. Automatically resume configured animation when last reserved pixel is released

Note: The above functionality is a pre-requisite to improving debug output. In particular, want to have assert() and hard_assert() handlers cause specific unique animation to make it clear there is a code issue (vs. hardware lockup), even with no debugger attached.