let getLocalizedPath on the i18n service return a promise.

[luxzeitlos]

The Idea is that the service can lazy load the translations from a backend, and then resolve then Promise.

[bcardarella]

@luxferresum failing travis

[luxzeitlos]

fixed. We still have the problem that if when u use the feature of returning a promise in getLocalizedPath then u will also get a promise when using the t util in code. There is just no way around this.