Technical Debt: Remove "PNG" and "png-encoder" libraries

[blockarchitech]

There are two very old and outdated JS libraries in use - png and png-encoder (one actually mentions 2011!). They are used in image.js for some utility functions, that power all images/icons used in Pebble.js.

Are we currently using features in the library worth having this old library for? Not to re-invent the wheel, but if all we need is some utility functions, I feel it is better to implement these than trying to maintain this old library.

Acceptance Criteria

• Seek replacements for the libraries, or upgrade them as seen fit.
• Identify if it is worth having the library in the first place.
  • As of current, it looks like it's only used in image.js.
• Remove the libraries, or upgrade them, based on the findings in AC 1 and 2.

Notes

It appears there's a ton of random color functions in image.js. Perhaps worthy of it's own ticket, but is that image.js's whole purpose? Could we not just move these functions to color.js and be done?