pgAdmin 4 commit: Resolved an issue about missing 'canDrop' function ch

Resolved an issue about missing 'canDrop' function check for the browser
tree nodes.

Each individual node is responsible for introducing the 'canDrop'
function/flag to decide whether the 'Delete/Drop' context menu should be
enabled/disabled.

In commit-id: 26aa5607ad8eb92591e732837e6aa1a0c48f62b3, 'obj.canDrop'
was set to true in the 'pgBrowser.Node' in delete callback, just to make
the server-group droppable, which is wrong, as all the nodes are
getting affected because of this change in a wrong way.

To fix the issue, added the 'canDrop' function in the server-group node.

Apart from them, also added restriction for not allowing to delete the
default server-group.

Also, handled the same restriction at the server end.

Branch
------
master

Details
-------
http://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=2c7a45814cd642cbe2c8b4364de392c4b00f841c
Author: Surinder Kumar <surinder.kumar@enterprisedb.com>

Modified Files
--------------
web/pgadmin/browser/server_groups/__init__.py                 | 10 ++++++++++
.../server_groups/templates/server_groups/server_groups.js    | 11 ++++++-----
web/pgadmin/browser/templates/browser/js/node.js              |  3 +--
3 files changed, 17 insertions(+), 7 deletions(-)