Add support for BaseUriPlugin plugin

[Nyholm]

Q	A
Bug?	no
New Feature?	yes
Version	next

The BaseUriPlugin is not supported by the bundle yet. We should fix that.

The implementation is very similar to how we do it with AddHostPlugin plugin.

1. First see "AddHostPlugin" documentation. (add_host)
2. Add an entry in plugins.xml
3. Update Configurations.php
4. Add the actual service declaration in the extension class.

@llaakkkk is that something you want to look into?

[llaakkkk]

great opportunity, I will do it!