feat #599 Adding a label.color state property.

The color of the label of most input widgets can now be defined
as a skin property, depending on the state of the widget.

In the atskin skin, the label of text input widgets and of the
select widget now show the disabled state with a different
color than the normal state. Moreover, the appearance of the
MultiSelect (especially for the focused state) is now more
consistent with other text input widgets.

Close #599
doc Commit message standards in CONTRIBUTING

Close #597.
fix #595 Wait Aria.load in test

There might be cases when a test starts an Aria.load but ends before the callback is called.
This causes undisposed objects and failures.

The commit modifies the test suite to wait for completion of Aria.load before actually ending the test and starting a new one.
fix #592 warning for deprecated jade feature

Remove warnings due to visionmedia/jade#1036
feat #602 Added HTTP methods for WebDAV support

All HTTP method specified by WebDAV can be used without errors, including
bind extensions

Close #602
fix #523 ellipsis bug fix + unit test

bug in the ellipsis element:
add an optinal property in aria text and sortindicator to compute the width that
prevents the text to get clipped.
feat #574 HTML select widget

The select widget has 3 properties:
- a list of 'options' to populate the select element
The user can bind to his data model:
- 'selectedIndex'
- 'value'

close #574
fix #605 HTML select widget: the 'value' property isn't properly bound

When binding only the value property of the html select widget, the
selected value was not correctly restored after refresh.
fix #609 Updating grunt to fix underscore.string issue with npm install

Grunt was relying on underscore.string version 2.2.0rc, but the version
number was renamed on npm to 2.2.0-rc (with the dash), which breaks
compatibility.
Merge branch 'master' into tests_dev