Add translatorNullInterpolator

Custom interpolation service for angular-translate that does - nothing.

Useful when we want to interpolate the strings ourselves.
Add nullInterpolator to $translationProvider
Return interpolate functions from translator
Make translator ultra-flexible

Now takes a string, an array of ids or an object with id mappings as
first argument.
First new usage of translator in globalSettings

Showcases the object usage and interpolation.
Use new translator in ArethusaCtrl

Showcases the usage with an array of ids.
Fix translations in artificialToken
Also interpolate with fns in translator
Change all to new translator syntax

Fixes a couple of trsl mistakes on the fly.
Return second argument in translator
Default second argument to {} in translator
And use once more simplified translator syntax
Start documention of translator
Finish translator documentation
Merge pull request #544 from latin-language-toolkit/translator_updates

Translator updates