Variety of adjustments to dropdown/menu behavior

- Removing use of drop.js library. I'm now just using the Tether.js
library to manage placement of dropdowns, but handling the open/close
myself to better control everything
- replace CSS-driven menu/tooltip animations with velocity.js animations
- reduce amount of code required to style dropdowns/tooltips;
animations are handled in JS
- all dropdowns/prospectus objects available on OSLC.dropdowns global
- replace Drop usage in tooltips
- replace Drop usage in Bartender
- Prospectus now has open() and close() that do something if the menu
is a dropdown
- add prospectus.options.isDropdown flag, along with cached control
element

related to issue #9
Expand $.toggleAria capabilities

$.toggleAria can now take multiple string attributes to toggle.

e.g. $(el).toggleAria('hidden','expanded') to flip both aria-hidden and
aria-expanded to their opposite current value

Related to issue #9