Rlecellier/dashboard teacher courses loading

[rlecellier]

note: this PR is made on top of #1951

Purpose

Add a loading effect on teacher dashboard course list page

Proposal

• useIsLoading: add minimum delay in order to see the animation. The idea is that it's better to see a loading effect during 0.5 sec than a instant blink.
• animate new page loading with a fade animation.

Todo

We need to choose:

• minimal loading time or not.
• wich effect do we want ? :
• • a page fade like in this PR.
• • a page grey overlay
• • a background blink on each glimps.