The options are not processed in the order I would like them to.
This means that it is not possible to have the default `titlelogo` and
`slidelogo` in the faculty theme (as they might be set before faculity
logo is defined). Users who would like the faculty `titlelogo` or
`slidelogo` should therefore explicitely require it.

I also made the `slidelogo=none` by default as I consider good practice
to de-clutter the content slides as much as possible.

BREAKING CHANGE: Changed defaults.

Signed-off-by: Thomas Lambert <t.lambert@uliege.be>