fix #945 Button text alignment in IE7

This commit fixes a problem on IE7 where text inside buttons is not centered.
doc Properties wrongly considered static in APIDoc

The documentation of the code is generated from JSDoc comments, which are parsed with an external tool. It is possible to document let's say detached properties, and to explicitely set their names with a special tag in the JSDoc. However, the tool in question uses this name to determine if a property is attached to an instance, a prototype or is static.

Therefore I prefixed the last part of the names with the proper container name when applicable:

- "prototype" for prototype members
- "instance" for instance members
- nothing for the others, which will be detected as statics (excepts for Aria members which are all considered to be in its prototype)

I took the opportunity to improve the documentation of the Modifiers class, explaining that modifier methods are not actually directly accessible.

Closes #947
feat #914 MultiAutoComplete Widget with more changes

Close #915
fix #948 ScrollableBodyTest

This commit fixes the following test:
test.aria.utils.overlay.loadingIndicator.scrollableBody.ScrollableBodyTest