Proposal Masked Input Widget

Feature : Masked Input Widget

I modified `lib/js/legady/widgets/form/fields.js` and added the file `lib/js/lib/imask.js`

For the inclusion of feature for masked input widget.
![New Contact 1](https://f.cloud.github.com/assets/1288676/76334/39787c52-60ea-11e2-9f28-5b5518755cad.png)
![New Contact 2](https://f.cloud.github.com/assets/1288676/76335/3da30aae-60ea-11e2-98d8-68e37a83d349.png)

Mask addition on Customize Form

![Customize Form](https://f.cloud.github.com/assets/1288676/78239/b2e9b50c-6175-11e2-8c48-2162667ccb56.png)