ui: Add email template & change model for author_user

Notice that old notification have to be removed or updated.

Adding author_user as a foreign key allow to use author information on email & to delete notification on cascade when author is removed avoiding incomplete datas.

Still no idea how to make a simple "Click to respond" link. May need a custom setting with some urls.

added 3 commits

• 69bdfb2c - 1 commit from branch master
• 0c98da1c - fix: author_user
• 90e3e71d - fix: user on distant server

Compare with previous version

added 2 commits

• 615f36b5 - 1 commit from branch master
• c20077cd - Merge branch 'master' into 'jbpasquier/template-mail'

Compare with previous version

merged

mentioned in commit c32b9ec7