[IMP] When no stock moves, change whatever you want, otherwise no change at all for UoM.  #3440 Enhancement request richard-willowit

The default UoM can only be changed when there are no stock moves (or only cancelled ones), but to any category.
The purchase UoM can be changed whenever you want, but has to be in the same category as the default UoM.

Closes #3440

[IMP] When no stock moves, change whatever you want, otherwise no change at all for UoM.  #3440 Enhancement request richard-willowit

[FIX] Remove line

[FIX] Constraint should be applied when UoM or PO UoM is changed
[ADD] sale: option to install sale_layout from settings menu
[ADD] Add the website_links module.

This module tracks clicks in mass mailing mails and allow the generation of trackable links in a website interface.

Modules modifications
---------------------
Refractoring of the crm_tracking_* classes in a new module.

* Extract the crm_tracking_* from the crm module into a new module "utm"
* Remove the crm_mass_mailing bridge module
* New dependencies of mass_mailing and website_links to utm.
[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