Add BrowserNav in the translation system

[CyrilleB79]

Hello Tony

There is a recent discussion on the add-on mailing list regarding the add-on translation and the automatic translation system.
More specifically in this discussion, it appears that there is a will to have BrowserNav translated.

From what I have seen, here is the (non exhaustive) status:

1. The content of the locale folder is out-of-date. It contains old translations of IndentNav; probably here since BrowserNav's spin-off from IndentNav. This out-of-date content needs to be removed.
2. Not all strings are translatable. You will need to make them all translatable. @Surveyor123 had made a PR for this (add missing translatable strings #2), but it is out-of-date. If you lack of time to do the job, maybe he would accept to update his PR or to create a new one.
   For whoever do this job, also think to translator comments. It's not mandatory for add-ons but it may be a plus for translators.
3. You should update pythonSources in the buildVars.py to get all translatable strings in the .pot.
4. You finally have to ask for integration in the translation system on the add-on mailing list and when the nvdaaddons fork is created, you need to create an issue in nvaccess/mrconfig to ask for the add-on's inclusion in the translation system. See here for more details.

If you need assistance or lack of time, you may ask for help on the add-on mailing list. I hope someone can help.
Personally, I can provide advices, but do not have so much time to help more. If you ask for help and no one answers positively, I can reconsider to help more, provided you confirm that you will be interested (i.e. I do not want to lose my time).

PS: Nothing to do with this issue. But while at it, can you take care of updating the style.css to last versions as you did for your other add-ons (e.g. Tony's enhancements)? Thanks.