Bug white key strokes when placeholder empty

This PR fixes a bug, where if you have mask elements separated with spaces, doesn't create empty white spaces when nothing is types in input.

For eg. mask "9999 9999 9999 9999" have been cosign problems
![whitespace](https://cloud.githubusercontent.com/assets/9808320/5124804/36b471ae-7071-11e4-976e-52d84af81a23.png)

/cc @ryan-roemer @patrickkettner @per-nilsson
GLOBAL: `STRING.trim` fails in IE8/9 (http://kangax.github.io/compat-table/es5/#String.prototype.trim) Please switch to `$.trim` (http://api.jquery.com/jquery.trim/)