Add image to course "links" (links tool)

[ywarnier]

Is your feature request related to a problem? Please describe.
At the moment, a link can be published on the course homepage, but the image of the link is old, untasty and cannot be changed (so if you have several links, they all appear in the same way).

Describe the solution you'd like
Add the possibility for any link to have an icon in the right dimensions (like in the homepage icons update feature) to be published on the homepage. This should allow for cropping and removing the existing image to return to the default.

This would require an additional field in the c_link table (at a minimum) and the synchronization with the c_tool table.

[Reference: BT#12205]

[christianbeeznest]

It is implemented in this PR #6039

Thansk for confirmation.

[ywarnier]

The checkbox "Add to course homepage" should appear last, so the icon upload button can appear right after it.