Make design improvements to Custom Fonts

Mentioned in https://gravityof.wordpress.com/2015/12/18/improving-custom-design-on-wordpress-com/.

Potential design improvements:
- Sort fonts by styles
- Make fonts searchable
- Allow greater customization of font styles (maybe an "advanced" mode)
- Make font schemes
- Potentially explore a way for basic text positioning to be manipulated, or even hidden entirely, in the Customizer (maybe in a future version of the Customizer)

This is mostly a placeholder issue, but can also be a good place to discuss ideas.

Review the linked WordPress.com design post and the Customizer context first. This placeholder lists sorting, search, advanced styles, font schemes, and text positioning as separate ideas, so one agreed scope and acceptance criteria are needed before locating implementation files. Done means a selected improvement has defined behavior and an agreed feasible plan.

Written by the indexing model from the issue text.