[FIX] website_forum - replace texttext by select2 for the tags fields
[FIX] website_forum: add fake tour for people waiting the tour. To remove in master. Without it, localstorage loop to search this unexisting tour after the install...
[FIX] doc: latex building

* add latex support for exercise admonition
* latex freezes/crashes on {HEAVY WIDE-HEADED RIGHTWARDS ARROW} so
  replace them by more manual arrows
* add some preamble configuration, may not even be necessary
* generate WS setup code only in HTML output. WS doc in latex still
  isn't great as it displays all 4 languages one after the other,
  ideally they should be tagged or something, so only one language at a
  time is generated in non-HTML outputs
[MERGE] forward port of branch 8.0 up to 5ed0739
[FIX] web_tip: prevent useless calls to eval_tip
[FIX] web_tip: properly remove the tip popover
[FIX] doc: double period in footer
[FIX] doc: incorrect class access in new api guide

When creating a class with the new API, we should use models.Model
instead of just Model.

closes #3713
[FIX] website_forum: use common method to compute tags for orm
[FIX] im_chat : momentjs undefined on external pages. Temporary fix by replacing moment() by window.moment(). The moment helper is defined in core.js, which is not imported in web_assets common. If refactoring, the dates will be pre-process in render_messages().
[MERGE] forward port of branch 8.0 up to fc329b6
[MERGE] forward port of branch 8.0 up to c41109f
[FIX] Add missings files from previous forward port.
[IMP] website_forum: add a new karma to control the
way links displayed in posts and answers. A nofollow attribute is
added is the author has not enough karma, adding a protection for
spammer tryign to improve their SEO.
[IMP] productbetter menutips and help for product menus.
[IMP] base, ir_sequence: added use_date_range field on ir.sequence, that allows to have several sequences running for the same one depending on date ranges (similar to what was existing previously on accounting with FY, which is now deprecated) + port to new API
[FIX] web_tip: tip repositioning

* call reposition when editable list view is rendered
* also reposition the popover when reposition is called
[FIX] web client fix: crash when loading translation

Problem happens when the user from the website tries to load a translation,
it opens up a modal window without an action.  But the modal has a (hidden)
searchview which tries to load custom filters corresponding to that
non-existing action.

Another problem at the same time was that the view manager could not
display the breadcrumbs for a non-existing breadcrumb.
[FIX] update tests and change search logic (webclient)

previous commit broke some tests.  The issue is that the search view
now avoid making requests if there is no action id.  But this is an
assumption that tests use, so some slight adjustments have to be made.

Also, this is the moment to give properly the action id to the favorite
menu.  Instead of bypassing its parent, it now receives the action id
from the search view.
[IMP] portal_sale, sale, website_quote: display the payment
button in emails only if there is an amount to pay. Free orders
exist (free events for example).

[IMP] website_sale: pay now is now confirm order if the sale order
amount is 0. Also improved the confirmation message in the checkout
process.