Remove default WordPress themes and plugins

[rafalgic]

I think that we should get rid of the default WordPress themes - they take space and most of the time aren't even used and (most probably will never be).

Similarly Akismet and Hello Dolly are barely ever used (the latter - probably never). Let's get rid of them, hmm?

[luboskmetko]

Sounds like a good idea to me. Moreover they always report updates available in WP admin which is a bit annoying.

[rafalgic]

I'm not sure how to do it, so feel free to assign to anyone else.

[luboskmetko]

I guess this will be done during installation using WP-CLI.

@jakub300 can you take a look on this when you have time? Thanks