pgAdmin 4 commit: Introduced the VariableControl, which will be used in

Introduced the VariableControl, which will be used in role(s),
database(s), and tablespace(s).

Thanks Harshal Dhumal for sharing the original patch.

I've modified a lot to work by fetching the variables later by giving a
url.

Also,
- Introduced the template macros for SECURITY LABELS and VARIABLES.
- Improvised the Backform.Control with better syntactic approach.
- Introduced a jquery function pgMakeVisible(..) to make it visible
under any obj which can be identified by unique class.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=1ba9067c606a4b065cf5e46c92194e3707c9b8d8

Modified Files
--------------
.../browser/server_groups/servers/__init__.py | 5 +
.../server_groups/servers/static/js/variable.js | 562 +++++++++++++++++++++
.../servers/templates/macros/security.macros | 6 +
.../servers/templates/macros/variable.macros | 6 +
web/pgadmin/browser/static/js/node.ui.js | 166 ++++--
web/pgadmin/static/css/overrides.css | 52 +-
web/pgadmin/static/js/backform.pgadmin.js | 398 +++++++++------
web/pgadmin/static/js/backgrid/backgrid.pgadmin.js | 2 +-
8 files changed, 1001 insertions(+), 196 deletions(-)