pgAdmin 4 commit: Added new url rules for each node by change NodeView

Added new url rules for each node by change NodeView class:
- Renamed the URL 'nodes' to 'children', because - we'll return the
children for the current node.
- Using the URL 'nodes' to fetch all nodes of its type, when not
specified the node-id, otherwise regenerate that node info using the
node-id (it will be used by the refresh function).

- Added the URL 'msql' for fetching modified SQL for the modified
objects.
- Separated the URL 'deps' (GET/POST methods) to 'dependency' and
'dependent', because - it will be used to fetch the properties of the
object, not manipulate it. (as suggested by Dave).

This commit includes the changes related to it in the specific nodes.
(i.e. server-group, and server).

Also, includes a javascript change to ask the user (if they really want
to leave the page, and it is not an accidental navigation by keyboard
shortcuts).

Branch
------
master

Details
-------
http://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=6d46dfbfba21c0e15a2f81d3f349db56dff9b2c8

Modified Files
--------------
web/pgadmin/browser/collection.py | 34 -------
web/pgadmin/browser/server_groups/__init__.py | 39 +++++++-
.../browser/server_groups/servers/__init__.py | 100 ++++++++++++++++++--
.../browser/templates/browser/js/browser.js | 16 +++-
.../browser/templates/browser/js/collection.js | 2 +-
web/pgadmin/browser/templates/browser/js/node.js | 5 +-
web/pgadmin/browser/utils.py | 50 +++++-----
7 files changed, 174 insertions(+), 72 deletions(-)