fix #746 test.aria.widgets.issue746.SkinClassFallbackTestCase

test.aria.widgets.issue746.SkinClassFallbackTestCase now passes both
in packaged and unpackaged modes. In unpackaged mode, it now tests the
right thing.
feat #790 Updating the computeSize method in order to consider borders

Updating the computeSize method in order to consider borders and margins.

Close #790
feat #781 CSS Gauge progress bar

Adding the css to be used to make the gauge progress bar instead of using images and sprites.

Close #781
feat #786 Adding skinnable properties for the icon

Close #786
fix #780 Removing overflow property from Select Widget style

Removing the overflow:hidden property from the CSS template of Select widget
feat #779 Adding the new AT flat skin

New flat skin for aria templates

Close #779
feat #791 add async-aware `beforeClass` and `afterClass` in TestCase

Apart from long-existing `setUp` and `tearDown` that are executed before
each test method, adds other JUnit-inspired `beforeClass` and `afterClass`
which make it possible to execute heavy methods only once.

The main added value is the possibility to do the things asynchronously
here (otherwise it could have been done in `$constructor`). Could be
useful e.g. to load a big JSON in `beforeClass` and then write normal sync
tests, instead of forcing the developer to load the JSON and continue in
the callback function.

The `beforeClass` and `afterClass` automatically infer if they're called
in asynchronous or synchronous way based on the number of arguments
received (0=sync, 1=async), to reduce the boilerplate code.