Added support for radio buttons group validation

Validates radio buttons group, and puts the (.xt-error) class and the tooltip on the element that is declared on the (data-val-cont="containerId") of the radio element.

In addition, the code throws an error if the developer forgets to add the (data-val-cont) attribute.
Merge branch 'master' of http://github.com/idreeshaddad/xtform into idreeshaddad-master

Conflicts:
	xtForm.js
Merge branch 'idreeshaddad-master'
refactor: allow for a data-tooltip-element attribute to specify tooltip element

 - This replaces the custom code for radio buttons and ui-select2 elements
 - Closes #13
chore: bump version