Updating the slug field to use the pyro.generate_slug slugify wrapper.

Fixes #2178.
Streams core does not need a readme file.
Fixing some instances where file functions were checking for a numeric ID.

Now that the ID is a 15 character string, we can no longer rely of checking if it is numerical or now.

Fixes #2172 and #2171.
Making sure we have the chunks field type if we need it in the page types admin area.

This was causing some errors when it was looking for the name of the chunks field type.
Merge remote-tracking branch 'origin/2.2/develop' into feature/bug-fixes