Mask formatter collision

This is an implementation to deal with https://github.com/angular-ui/ui-utils/issues/139. Essentially the problem is different `formatters` conflicting with eachother. There are many ways to 'solve' this problem, the one implemented in this pull request checks if a `formatter` exists apart from the one used `ui-mask`, if more formatters exist, then the formatter will return the original value, instead of the one created by `maskValue(value)`

This means that if you only use `ui-mask` with no other formatters, it works as intended, but if you use `ui-mask` with other formatters, it won't return the remasked value.

Test cases have yet to be written as I am waiting on feedback if this is the ideal way to solve this problem