[FIX] Multiple report fixes including better handling of rendering a report with one worker (and the removal of the workers creation) and some report views changes (address block more to the left)

Improve handling of website image fields

I have no idea why I originall implemented that crap via string munging.

[MERGE] website_mail_group: cleaning and usability improvement of this web module
- refactored the website templates that were basically impossible to use
- fixed display by thread / date and navigation
- added information about group email, participants, messages, ...

[IMP] website_mail_group: display previous / next message when browsing + take into account thread or date mode.

Some fixes in the image qweb widget + CMS fixes

[FIX] website_mail_group: effectively handle replies_per_page parameter that controls the number of replies to display under each message.

[FIX] website_mail_group: better layout for main mailing lists page: more space for subscribe button

[MERGE][FIX] website_event_track: display speakers name to public users

1st issue:
When an exception was raised, it was badly handled by the website in case of
website_enabled key. The response page was generated without calling super.
The WebRequest object being responsible to rollback the transaction in case
of errors.

2sd issue:
The _failed attribute is required to rollback the transaction in an WebRequest
object. Previously it was only set in the JsonRequest object (which inherit
from WebRequest), replace by call to super. The attribute _failed is now set
in the WebRequest object.

[IMP] [BACKPORT] Converto bzrignore to gitignore, like what has been done in master.

[IMP] website_mail_group: refactored layout of displayed mailing lists and their archive. Should be a bit more easy to use and understand. Todo: fix number of displayed thread / replies, and probably re-do the layout once somebody decides to change everything.

[FIX] ir_actions: adapt render_report when called in a tests/qweb report context to generate the pdf only if a directory has been provided

[FIX] Report: inform the user that he may not print a pdf report while his openerp is running with only one worker; adapt method to extract wkhtmltopdf version to also work on mac where the ouput of '--version' is different from gnu/linux binary

[FIX] Report: double the default height/width of barcode image to avoid a blurred/unusable barcode once integrated in a report