pgAdmin 4 commit: Introduced a class - NodeView to achieve REST API req

Introduced a class - NodeView to achieve REST API required by the
PostgreSQL node(s).

Browser Tree Node (PostgreSQL object) requires more than just CRUD.
i.e.
   - CRUD (Create, Read, Update & Delete)
    - Reversed Engineered SQL for the object
    - Modified Query in edit mode
      i.e. ALTER TABLE ...
    - Statistics
    - List of dependents
    - List of dependencies
    - Children node list

This class can be inherited to achieve the different routes for each of
the object types/collections.

    OPERATION      |              URL       | Method
    ---------------+------------------------+--------
    List           | /obj/[Parent URL]/     | GET
    Properties     | /obj/[Parent URL]/id   | GET
    Create         | /obj/[Parent URL]/     | POST
    Delete         | /obj/[Parent URL]/id   | DELETE
    Update         | /obj/[Parent URL]/id   | PUT

    SQL (Reversed  | /sql/[Parent URL]/id   | GET
    Engineering)   |
    SQL (Modified  | /sql/[Parent URL]/id   | POST
    Properties)    |

    Statistics     | /stats/[Parent URL]/id | GET
    Dependencies   | /deps/[Parent URL]/id  | GET
    Dependents     | /deps/[Parent URL]/id  | POST

    Children Nodes | /nodes/[Parent URL]/id | GET

    NOTE:
    Parent URL can be seen as the path to identify the particular node.

    i.e.
     In order to identify the TABLE object, we requires information
     about the server -> database -> schema objects.

     Hence, the Parent URL for the TABLE object will be something like
     this as below:
     <int:sid>/<str:database>/<str:schema>

Inherited a new classes ServerGroupView and ServerView, which are
inherited from the NodeView for the implementation of above operations.

Branch
------
master

Details
-------
http://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=35d01bea3ebda80f0e52e55446b34e3950452986

Modified Files
--------------
web/pgAdmin4.py                                    |    4 +-
web/pgadmin/browser/__init__.py                    |   37 ++-
web/pgadmin/browser/server_groups/__init__.py      |  225 +++++++++------
.../browser/server_groups/servers/__init__.py      |  301 ++++++++++++++------
.../servers/templates/servers/servers.js           |   32 ++-
.../templates/server_groups/server_groups.js       |   23 +-
web/pgadmin/browser/templates/browser/css/node.css |    2 +-
.../browser/templates/browser/js/browser.js        |    6 +
web/pgadmin/browser/utils.py                       |  212 +++++++++++---
web/pgadmin/settings/settings_model.py             |   26 +-
web/pgadmin/templates/base.html                    |   24 +-
web/setup.py                                       |   13 +
12 files changed, 624 insertions(+), 281 deletions(-)