3.0.2

This is a bigger update than I like to do all at once, but I had to do a larger refactor to fix a few deep rooted bugs. There's a lot going on here but the basics are:

## Inside

- Moved grid-notation (formerly GuideGuide Notation, formerly GuideGuide String Notation) into it's own lib: https://github.com/guideguide/grid-notation
- Heavily refactored it, including:
  - Grid notation now respects resolution
  - Full positioning support, so that grids can be centered (previously impossible in conjunction with wildcards)
- Moved GuideGuide messages into its own lib: https://github.com/guideguide/messages
- Removed a bunch of unused code
- It is now valid to use percents that add up to more than 100%. If you want two 75% width columns, who am I to tell you no?
- Added localizations for midpoint checkboxes ([translations needed](https://github.com/guideguide/messages/blob/master/src/messages.coffee#L91-L98))

## Outside

- UI tweaks to scale down the panel a bit.
  - Smaller type
  - Tighter padding around inputs and buttons
- Reorganization of the settings page to avoid scrolling.
- Dropdown labels inside the dropdown rather than above.
- Fixed text overflow issues causing the panel to look terrible at small sizes or in languages with long text strings.
- Remove help descriptions from settings. If people find them too confusing I'll put them back.