pgAdmin 4 commit: Clear the node cache, when an node is created/updated

Clear the node cache, when an node is created/updated to make sure - we
will always have latest data related to that type of node. Also, fixed
the cache_level for different node types.

This commit also contains fixes for the following issue:
* In extension module - use the 'node-list-by-name' instead of using a
  custom 'node-ajax-options' control, and removed redundant template
  schemas from it.
* When we tries to destroy the select2 object from
  Select2Cell/Select2Control while releasing the properties view,
  sometimes select2 can not find the instance related it for some
  unknown reason. Hence - before removing it we will check for manual
  instance existance using $.data('select2').
* When we traverse through the browser tree nodes very quickly, it tries
  to remove the object before it gets created completely, and results
  into an exception.
* Icon in the select2 drop down list was not visible due to some CSS
  issues.

Apart of that, we will generate two new browser events -
'pgadmin-node:created:<NODE-TYPE>', 'pgadmin-node:updated:<NODE-TYPE>'
whenever a new node is created, or an existing node will be updated.

Branch
------
master

Details
-------
http://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=32e0a0d4b62462d45da88c177ffc6966de3dbcbb

Modified Files
--------------
.../templates/extensions/js/extensions.js          | 21 +++----
.../templates/extensions/sql/schemas.sql           |  3 -
.../collations/templates/collation/js/collation.js |  7 ++-
.../domains/templates/domains/js/domains.js        | 16 ++++--
.../templates/fts_dictionary/js/fts_dictionary.js  |  7 ++-
.../templates/fts_parser/js/fts_parser.js          | 18 ++++--
.../templates/fts_template/js/fts_templates.js     | 13 +++--
.../databases/templates/databases/js/databases.js  |  8 +--
.../templates/databases/sql/9.1_plus/nodes.sql     |  2 +-
web/pgadmin/browser/static/js/node.ui.js           | 32 +++++++----
web/pgadmin/browser/templates/browser/js/node.js   | 66 +++++++++++++++++++---
web/pgadmin/static/css/overrides.css               |  5 ++
web/pgadmin/static/js/backform.pgadmin.js          |  6 +-
web/pgadmin/static/js/backgrid/backgrid.pgadmin.js | 10 +++-
14 files changed, 148 insertions(+), 66 deletions(-)