Feature: bulk creation of bookmarks

This changes creates a new form in addlink page allowing to create
multiple bookmarks at once more easily. It focuses on re-using as much
existing code and template component as  possible.

These changes includes:
  - a new form in addlink (hidden behind a button by default),
containing a text area for URL, and tags/private status to apply to
created links
  - this form displays a new template called editlink.batch, itself
including editlink template multiple times
  - User interation in this new templates are handle by a new JS script
(shaare-batch.js) making AJAX requests, and therefore does not need page
reloading
  - ManageShaareController has been split into 3 distinct controllers:
    + ShaareAdd: displays addlink template
    + ShaareManage: various operation applied on existing shaares
(change visibility, pin, deletion, etc.)
    + ShaarePublish: handles creation/edit forms and saving Shaare's
form
  - Updated translations

Fixes #137