Atempt to simplify the configuration stack in CubicWeb

Related #476 (closed)

I've made the mistake to look at CW source code again, or was forced too, idk.

Anyway, I've made a map of all the weird configuration gigantic class stack we have in CW.

Here how it looks WITHOUT devtools:

And with devtools:

It's kinda overly complicated for no real good justification.

So I've decided to try to simplify it like that:

Which result in that:

And with devtools (which explains why I couldn't merge it even more) :

Since this is a lot of modification I've split it into parts because we might not want all of them or all of them at once, so commits are in this order:

1. merging CubicWebNoAppConfiguration into CubicWebConfiguration because it has no real usage
2. merging WebConfigurationBase into WebConfiguration because it has no real usage
3. remove the -c option to 'cubicweb-ctl create' which allowed to create CW using "repository.conf" or "pyramid.conf" but was in practice never used and we only use (I think?) "all-in-one.conf" today
4. this allow to remove CubicWebPyramidConfiguration because it's not used anymore
5. which allow to merge BaseWebConfiguration into WebConfiguration

I've used search-forge to see if any of the removed class are used somewhere and the only case is here:

• https://forge.extranet.logilab.fr/cubicweb/cubes/jsonschema/-/blob/branch/default/cubicweb_jsonschema/site_cubicweb.py#L35

For CubicWebPyramidConfiguration which just needs to be removed from this list.

So we'll probably won't have any real retrocompatibility issues.