[IMP] website_event_sale: validation of seats availability in cart.
Attendees are created and deleted on changing the quantity from the cart.

Added sale_order_id and sale_order_line_id fields on registrations, allowing
to find the order and the order line that created the registration without
to rely on origin and ticket.

Also fixed check_auto_confirmation, now in multi mode to avoid issues due to
the specific behavior of api.one.
[FIX] mass_mailing: updated link conversion.

Previously to this fix, url matching the same base url were linked to
the same shortened url: foo.be -> /aaa, foo.be/bar -> /aaa/bar instead of
a new shortened url.
[REM] hr_holidays: dead file
[FIX] mail : fix style (css, js and xml) of topbar button of mail.compose.message
[IMP] im_chat, im_livechat : usability improvements like, adding smiley, replace uuid by session name in reporting, modify messages order for the session form view and disabled beep when you receveive your messages.
[FIX] hr: fixed issue in employee image display in the kanban view
especially when using the group-by. Added a missing 'row', used an img-responsible
class instead of a fixed width.
[IMP][website_mail] improved template designer, added support for background color, font color and bootstrap buttons(inline css) in mail designer,removed other snippet, changed snippet according to new format,added theme selector in mail_designer, lodeded snippets dynamically based on theme, added font-awesome support in mail snippets, added one controller which convert font-awesome to icon

[IMP][website_mail] changed less colorpicker to inline ckeditor color picker

[IMP][website_mail] Improved discount coupon and image text snippets