pgAdmin 4 commit: This is a big one campers; Add initial support for tr

This is a big one campers; Add initial support for treeview nodes.

This commit adds the following:

- Storage of server groups in the configuration database
- Creation of a default server group on in the database
- A mechanism for plugging in treeview node types
- A node type for server groups with:
- Treeview display
- Custom per-node javascript implementing a menu option/dialogue to add new groups
- Custom per-node CSS to style the treeview node
- JSON formatted data in response to AJAX requests, including:
- Success/failure indication
- Error message
- Extra info (e.g. stack trace)
- The original request data
- Additional return data, e.g. node ID and label etc.

Branch
------
master

Details
-------
http://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=89cc11fb8075494160803a98e32a7c746c97ffcf

Modified Files
--------------
web/config.py | 4 +
web/pgadmin/__init__.py | 11 ++-
web/pgadmin/about/browser.py | 26 ------
web/pgadmin/about/hooks.py | 26 ++++++
web/pgadmin/browser/__init__.py | 11 +++
web/pgadmin/browser/hooks.py | 51 +++++++++++
web/pgadmin/browser/nodes/server_groups/hooks.py | 75 +++++++++++++++
.../server_groups/static/img/server-group.png | Bin 0 -> 504 bytes
web/pgadmin/browser/nodes/server_groups/views.py | 64 +++++++++++++
web/pgadmin/browser/static/js/utils.js | 39 ++++++++
web/pgadmin/browser/templates/browser/body.html | 13 +--
web/pgadmin/browser/templates/browser/index.html | 4 -
web/pgadmin/browser/views.py | 96 ++++++++++++++++----
web/pgadmin/settings/browser.py | 16 ----
web/pgadmin/settings/hooks.py | 16 ++++
web/pgadmin/settings/views.py | 51 ++++++++---
web/pgadmin/static/css/overrides.css | 18 +++-
web/pgadmin/test/browser.py | 27 ------
web/pgadmin/test/hooks.py | 27 ++++++
web/utils/ajax.py | 24 +++++
20 files changed, 483 insertions(+), 116 deletions(-)