Notify administrators when a license is about to expire

[aubincleme]

The idea is to avoid administrators discovering by surprise that the license for their pro extension just expired, and having to rush to the purchasing department to do all the paperwork eventually needed to renew the license.

We could display a first warning through the notification bell (much like what is done today when a license is expired) when a license gets to be valid for less than 15% of its validity period.