Sanitize abstractTextField propagated DOM value

In general, we don't want to present undefined, nulls, etc. as anything
more than empty strings.
Sanitize abstractTextArea propagated DOM value

Same behavior of the textField now, though they should probably share
a common base. It's suspicious that they don't at least share
abstractControl.
Merge pull request #1227 from mczepiel/text-field

Sanitize abstractTextField propagated DOM value
Add delegate methods to AbstractTextField
Let number field be delegate for text field; let user input non-valid string and move validation to end of editing
Add some specs for the AbstractTextField delegate.
Update specs to match current AbstractNumberField
Remove Modal properties from Overlay

A new ModalOverlay component will be created to address modals.
Add missing Overlay HTML
Merge branch 'master' of git://github.com/montagejs/montage into super
Change super cache to just store reference to super on method