reviewers: store additional review data. G: changed rhodecode/model/db.py

features: show new review rules in CE default reviewers

pull-request: extended default reviewers functionality. - added mandatory reviewers JS logic Fixes: #4219 - added option to forbid author to be a reviewer via JS/Frontend checks. Fixes #5190 - added option to forbid adding new reviewers except those defined. Fixes #5208

user-autocomplete: allow skipping default user.

reviewers: moved the new v1 api of default reviewers into pyramid view. - updated schema - updated logic of routing so EE can override it.

pull-requests: moved the listing of pull requests for repo into pyramid. - moved as datagrid App - changed loading of grid to lazy, as other new views.

maintenance: added svn verify command to tasks to be able to verify the filesystem and repo formats.

permissions: move refresh operation as a flag to the get_default_user function

templates: expose default user data into templates for JS usage.

log-in: changed naming from log-in to sign in for consistency with other text.