[FIX] website_forum: new batch of fixes :
- fixed reopen link that was broken (python code appearing)
- fixed close link that was leading to a 500 error due to post -> question
- fixed link to question author, was redirecting to the current user
- fixed displayed number of questions in the forum, now displaying actual question
number, not number of displayed questions in the page
- improved guidelines: added link back to the forum
- fixed tags display: now by posts_count desc, unused tags are not shown
- users are now displayed by desc karma
- converting a comment as an answer does not allow to create a new answer if another
one by uid is already present, it just moves the comment
[IMP] gamification: performance improvement on the goal computation

Removing the inheritance to mail.thread will avoid posting message at creation and other tracking mechanism at each write. Updating a challenge with a large number of users will be significantly faster.
[FIX] gamification: avoid recomputing every goal for every challenge
[IMP] gamification: move write in goal update inside the first loop to be able to group the computation by definition (and potentially apply intermediate commits)
[IMP] gamification: commit for each goal definition in cron
[FIX] gamification: be sure that not challenge get subscribers depending of the report_message_frequency
[FIX] website_forum: more fixes :
- display tag name in 'filter' bar when filtering on a tag
- display active tag in a blue color
- order answers: correct first, then most upvoted
[FIX] gamification: using batch mode to check rewards
[IMP] unsubscribing at each cron run is overkill
[FIX] name_get returns tuple
[REF] gamification: performance improvements when running with a large number of users

- gamification.goal do not depends of mail.thread anymore (message posting and fields tracking was slow)
- check reward works in batch mode
- fix update method that did not reset variable in loop
- when the cron is running commit after each goal definition update
[MERGE] [FIX] website_forum: batch of fixes :
- fixed reopen link that was broken (python code appearing)
- fixed close link that was leading to a 500 error due to post -> question
- fixed link to question author, was redirecting to the current user
- fixed displayed number of questions in the forum, now displaying actual question
number, not number of displayed questions in the page
- improved guidelines: added link back to the forum
- fixed tags display: now by posts_count desc, unused tags are not shown
- users are now displayed by desc karma
- converting a comment as an answer does not allow to create a new answer if another
one by uid is already present, it just moves the comment
- display tag name in 'filter' bar when filtering on a tag
- display active tag in a blue color
- order answers: correct first, then most upvoted
[FIX] account_analytic_analysis: recurring invoices, map_tax and map_account methods of fiscal position model expect a browse record