Doc should mention libapache2-mod-wsgi-py3 dependency

[regisrob]

... as it seems to be required to run Loris > 2.3.3 with Apache. Installing libapache2-mod-wsgi-py3 solved #533.

So apache.md and dependencies.md should be updated to mention this dependency, depending on the version of Loris (but I guess libapache2-mod-wsgi-py3 should be the default and recommended one).

I'd be happy to make a PR for that if it is a valid assertion.

[bcail]

yes, Loris doesn't support python 2 anymore, so all docs should reference python 3 packages (unless there's a note with the python 2 package that it only works for old versions of loris). A PR would be welcome.