Refactor and expand selection core mixin.

Harden select helper and add selectByClass helper.
Refactor tip plugin's core scss.

Improve balance between conveying DOM hierarchy
and selector specificity.
Allow tip instances to be mixin-compatible with _setTip.
Add core selection mixin to tip instances.

Also refactor _inflateByTrigger.
Refactor numeric css access in tip plugin...

Note I wrote an entire $.cssNumber aspect to the
core extension to get certain properties to always
return numeric, before realizing it cssNumber
wasn't fully implemented and $.css, despite being
unpublished API, was another route.
Fix Grunt watch:css subtask to work with copy:css.

Otherwise scss don't get copied to dist on update.
Add initial tip resize CSS transition...

This commit starts the series for animation
support.

Also includes a substantial update of
sizeForTrigger with refactoring and support for
getting the tip content size.
Fixup event extension namespace helper.