runtime: Account nicknames (#3930)

* Add Nicknames module for accounts.

* Integrate into node.

* Fix build

* Update srml/nicks/src/lib.rs

Co-Authored-By: Kian Paimani <5588131+kianenigma@users.noreply.github.com>

* Bump runtime

* Improve weight docs

* Docs.

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>