Blogs: some rewrites rules are missing & the create action is not implemented

[imath]

In multisite, the Blogs component generates a directory page and a route to create a new site if the Network Admin allowed it. When working on #4954, I forgot to generate custom rewrite rules for directory action or action variables (even if we do not support them for our needs) and to parse the create new site request.

Add missing rewrite rules and create route requests parsing

Trac ticket: ​https://buddypress.trac.wordpress.org/ticket/8925

[imath]

In 13505:

Blogs: implement Action, Action variables & Create rewrite rules

These rules were missed in #4954

Fixes #8925
Closes ​https://github.com/buddypress/buddypress/pull/119