Add new chip input and chips

[mdo]

This adds a new .chip and .chip-input component. The individual chips are derivative of badges, but not a 1:1 match. Chips are built to utilize theme classes, has specific styles for each state (default, selected), and comes with some automatic behavior vs JS for the chips input (which wraps the chips and a ghost input).

• Type and Enter to add a new chip in a chip input
• Backspace from input selects previous chip, backspace again deletes it and focuses on next nearest chip
• Clicking a chip in a chip input focuses that chip
• Chips use subtle/text theme keys first, and for selected use bg/contrast
• Chips can include text, images, icons, and dismiss button

An open question I have is, do these usurp badges entirely? Should badges turn into little adornments absolutely positioned on an element only? Or like inline counts?