feat(ngTouch's ngClick): add 'ng-touch' attribute with value of 'keep-focus' to prevent bluring

Can now add 'ng-touch=keep-focus' to any element to prevent the focus from being blured.
Primarily useful for input elements in a modal where one needs the soft keyboard to remain open or
for select elements.  Without the new attribute, select elements are difficult to use under iOS when
the element is on a modal and input elements that depend on the soft keyboard were unusable.  Now
with the new attribute, they are fully usable.  If the new attribute is not used, old behavior is
mantained.