Markers customization

[nrslt]

Hi guys,
I just wanted to quickly add the new markers to this existing PR.

• blue one with tower icon = site marker
• red one with Pyronear icon = alert marker
• grey one with Pyronear icon = old fire marker

at this point it looks like this:

To improve these, we will need to:

• rethink clearly the way we want to display alerts + sites,
• monitor the iconAnchor parameter so that the tip of the icon is correctly placed on the right coordinates (still unclear how this parameter behaves),
• change the iconURL path

[Akilditu]

• iconURL path

Indeed this would be a good idea to host those icons somewhere else that in assets folder.
@frgfm maybe as we did for logos under pyronear.org ?

[Akilditu]

Thanks a lot for this PR !

Could you please resolve the 2 following flake8 errors :

./app/alerts.py:114:55: E261 at least two spaces before inline comment
./app/alerts.py:155:56: E261 at least two spaces before inline comment

[frgfm]

@Akilditu yup, I think that would be the best thing to do 👌
We can also make a mock release on the website repo, and put all logos in the attachments! Whichever you think is best

[frgfm]

@nrslt if the reason the PR was closed is only about updating the branch, you can merge master (or another branch for that matter) ;)
Would be better than reopening the same PR