doc Improve Aria.load method documentation

Close #943
Always register a binding to section processing

If section processing is not bound to any data model, a spinner overlay created using setProcessingIndicator on the SectionWrapper does not follow it as one of its parent is moved and not closed if the section is deleted. Thus if the user does not specify any binding the overlay remains at its initial place forever.

Binding it to a dummy container allows both of the shortcomings to be solved: spinner follows its parent section and is closed upon section removal.
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