fix #570 Wrong content type in IE 8 with asyncFormSubmit.

In IE 8, setting the enctype attribute of a form with the
following line does not work:
 form.enctype = value;

The following line works better:
 form.setAttribute("enctype", value);
fix #572 Exception when accessing history.state in IE 10

Accessing history.state sometimes raises an exception in IE10,
instead of returning null.
This fix surrounds accesses to history.state with try / catch
blocks.
fix #571 "this.__delegateMapping is null" when unloading a page

The exception "this.__delegateMapping is null" could happen in some
cases when unloading a page. This commit fixes this small issue.
fix #573 Style tag reload for html:Template

Calling the getCSSClassNames method of the template context in the initWidget of the html:Template widget was causing a further style tag reload, with a significant performance degradation.

Storing the classnames while writing the markup allows for an optimization of style tags reloads, which is done through the CSSMgr stop/resume mechanism.
refactor moving remaining tests

Publish all other widget tests

Close #549