Convert styles to LESS and implement grunt task

Styles:
* Use a variety of LESS features
* Lower browser requirements to IE8 or so

Also:
* ToggleSwitchWidget: renamed $on to $glow, $on was a bad choice given
  methods and states with the same name
* OptionWidget: Removed initialization of highlighted and selected - these
  states are managed by the SelectWidget so using them would actually
  cause it to be out of sync - and we of course don't even use these
  useless options anywhere so it's not a breaking change

Gruntfile:
* Implement less compile and dist in Grunt.
* Known issue: Though @noflip and @embed are preserved, it
  seems both in ruleset and declaration comments a new line
  is added after the comment, may or may not be a problem.

Change-Id: Iabb05703978e90fb9cac5ea1ffd453e7c402c0f1
Add documentation for -1 tabIndex option, which disables tab indexing

Change-Id: Id752807457f21e7fa97d97489e189ce33fc68460
Manage active state of BookletLayout pages

* Always detect page changes using focus tracking, not just when outlined
* Set mutually exclusive active state on pages
* Toggle activity class on pages

Change-Id: If058e1077a23daec68decf0e4bfdbc392667525c
Disable vertical scrolling in continuous layout mode

Change-Id: I5c09ea3c1f1a02b2e496d175a10b8fc846cc84a3
Make text inputs gray when disabled

They just looked too similar to enabled ones.

Change-Id: Id0f7afa95e2f6db2a52dc2c58c80f31f8832488f