This is the first commit doing mainly 3 things:
1. create a new scope and allow users to use it
2. Have the JWTController respond correctly on this
3. Updates documentation to suggest usage of PATs

There is one gotcha, there will be no support for impersonation tokens, as this
seems not needed.

Fixes gitlab-org/gitlab-ce#19219

This Cop blacklists the use of ActiveRecord's "serialize" method, except
for cases where we already use this.

Gitlab::Auth and API::APIGuard already check for at least one valid
scope on personal access tokens, so if the scopes are empty the token
will always fail validation.

- Use `TokenAuthenticatable` to generate the personal access token
- Remove a check for `authenticity_token` in application controller;
  this should've been `authentication_token`, maybe, and doesn't make
  any sense now.
- Have the datepicker appear inline

- Show the count for each section in parens
- Remove the `revoked?` check, because everything in the
  active section is guaranteed to not be revoked.