Add About dialog (w/ default styles) and clean up Builder

* Update/add i18n keys to use in Builder template instead of hard-coded strings
* Clean up Builder instantiation code and old About logic
Done button: make position and size consistent

(Fixes positioning in Firefox)
Builder: Fix legend color in IE
Builder: Improve column add/remove APIs and add 2 by default
Builder: Clean up tab styles and fix column editor in Safari

Safari issue was due to lack of vendor prefixes; fixed with nib/vendor
Builder: Resolve scrolling issues in control panel

* Use dgrid-autoheight and SingleQuery mixin for the column/feature grids
* Simplify CSS
* Remove transform/transition for now since it complicates scrollHeight issues
  in column grid