Internationalized strings are still missing the possibility to host variables

[evilaliv3]

Since ever GlobaLeaks translation feature is missing the possibility to host variables inside translation sources.

This is since always representing a limit for usability of the app and is becoming more and more needed now that the target is to develop a rich client with input validators, user indicators about time and counters that would require parameterized strings.

As reference for example would be needed for implementing features like #1351 with a rich translation with respect to all the different languages an not only to Italian/English where the grammar is somehow easy and its not so difficult to attach a number to a string making it appear somehow a good translation.

[evilaliv3]

Done!

now we have a file dynamic_strings where we can put strings that host dynamic variables.

it is already hosting two strings needed for fields validation: https://github.com/globaleaks/GlobaLeaks/blob/a1b5305fdd8053bac3eef5c797f59fddc6b86585/client/app/data/dynamic_strings.json

what changes for this strings is the way they should be written inside angular templates so that what i've to create for them is a special way to push them on transifex and refetch them.