Adding translated markers and custom missing prefix.

We wanted an easier way to make sure all of the text on a page is being passed through angular-gettext. 

This PR puts new properties on the `catalog`:
`showTranslatedMarkers` - whether to wrap all processed text
`translatedMarkerPrefix` - defaults to `[`
`translatedMarkerSuffix` - defaults to `]`

We find it is much quicker in testing.

Additionally I went ahead and made the `[MISSING]: ` text configurable via a `debugPrefix` property. The reason is that we wanted to have a version without a space in it, such as `MISSING_` or `?:`, to prevent wrapping issues we had in testing. 

I added some unit tests, let me know if there is anything else I should do for this. Thanks!