Abstract classes must have prefix Abstract

[xepozz]

PSR Naming Conventions says:

Abstract classes MUST be prefixed by Abstract: e.g. Psr\Foo\AbstractBar.

I think we need to fix it in the same way as interface naming conventions is fixed

[samdark]

PSR naming conventions are not about userland code style, they are about code style to use in PSR documents. We currently do not prefix abstract classes and I see no need to do so.