[Css] Add addCls() and removeCls() methods to the jqc.util.Css singleton, for adding and removing CSS classes from a string of CSS classes.
[Component] Use new jqc.util.Css methods, addCls() and removeCls(), for Component's own addCls() and removeCls() methods.
[Css] Add hasCls() method to jqc.util.Css singleton, for testing if a string of CSS classes has a given CSS class within it.
[Component] Update Component's hasCls() method to use the jqc.util.Css singleton's hasCls() method when in its unrendered state.
[Panel] Add `bodyCls` config, as well as addBodyCls(), removeBodyCls(), hasBodyCls(), and setBodyStyle() methods to Panel.
[Css] Add a few extra tests to check that the jqc.util.Css.hasCls() method does not return true for substring CSS class name matches.
[TabPanel] Have the TabPanel add specific "child panel" CSS classes to the child panels which are added to it. This is to allow for specific styling of Panels which are direct children of a TabPanel.
Rename all CSS classes that had UpperCamelCase CSS class names (for those which represented JavaScript classes), to lowercase.

This was done to remove the possibility of the problem that something is not a class name at some point (like "panel-header"), and then is upgraded to be its own class at a later date. To maintain consistency, the CSS class name would have to be renamed to "panel-Header", which cannot be done while maintaining backward compatibility.