Contact Member's Block: handle message between 2 members of the site.

imath

- [x] Create a new email template - [x] Localize display name and email - [x] Add a `current_user` attribute to the `sent_item()` method and adapt it.

imath

This commit https://github.com/imath/reception/commit/44cf2785c83c25dc9d501b94e34c5a5adce741d0 should be referenced here.