LPS-34905 as new attribute in aui:input

Hi Julio, 

I've tested your changes and they work as expected. I made only 2 slight changes:
(1) added constant field for the name of the pref key, where the dimensions are stored.
(2) when the textarea is not resizable, dimensions are neither fetched nor applied on the textarea (using style="...") -- this will allow the developers to make textarea non-resizable with no dimensions applied, without the need to remove-and-add the portlet to the page (to reset the portlet prefs) 

Thanks!

Josef