pgAdmin 4 commit: Handling the bad/lost connection of a database server

Handling the bad/lost connection of a database server.

Made backend changes for:
* Taking care of the connection status in the psycopg2 driver. And, when
the connection is lost, it throws a exception with 503 http status
message, and connection lost information in it.
* Allowing the flask application to propagate the exceptions even in the
release mode.
* Utilising the existing password (while reconnection, if not
disconnected explicitly).
* Introduced a new ajax response message 'service_unavailable' (http
status code: 503), which suggests temporary service unavailable.

Client (front-end) changes:
* To handle the connection lost of a database server for different
operations by generating proper events, and handle them properly.

Removed the connection status check code from different nodes, so that
- it generates the proper exception, when accessing the non-alive
connection.

Fixes #1387

Branch
------
master

Details
-------
http://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=f12d981a9d24d9d3725f7d51d99706fa211c7938

Modified Files
--------------
web/pgadmin/__init__.py | 1 +
web/pgadmin/browser/collection.py | 3 +-
.../browser/server_groups/servers/__init__.py | 57 ++--
.../server_groups/servers/databases/__init__.py | 326 ++++++++----------
.../servers/databases/casts/__init__.py | 48 +--
.../servers/databases/event_triggers/__init__.py | 21 +-
.../databases/foreign_data_wrappers/__init__.py | 18 +-
.../foreign_servers/__init__.py | 19 +-
.../foreign_servers/user_mapping/__init__.py | 19 +-
.../servers/databases/languages/__init__.py | 19 +-
.../servers/databases/schemas/__init__.py | 14 +-
.../databases/schemas/catalog_objects/__init__.py | 13 +-
.../schemas/catalog_objects/columns/__init__.py | 13 +-
.../databases/schemas/collations/__init__.py | 17 +-
.../servers/databases/schemas/domains/__init__.py | 17 +-
.../schemas/domains/domain_constraints/__init__.py | 20 +-
.../databases/schemas/foreign_tables/__init__.py | 14 +-
.../schemas/fts_configurations/__init__.py | 25 +-
.../databases/schemas/fts_dictionaries/__init__.py | 21 +-
.../databases/schemas/fts_parser/__init__.py | 20 +-
.../databases/schemas/fts_templates/__init__.py | 35 +-
.../databases/schemas/functions/__init__.py | 24 +-
.../databases/schemas/sequences/__init__.py | 43 +--
.../servers/databases/schemas/tables/__init__.py | 29 +-
.../databases/schemas/tables/column/__init__.py | 17 +-
.../constraints/check_constraint/__init__.py | 14 +-
.../constraints/exclusion_constraint/__init__.py | 16 +-
.../tables/constraints/foreign_key/__init__.py | 50 +--
.../constraints/index_constraint/__init__.py | 15 +-
.../templates/constraints/js/constraints.js | 4 +-
.../databases/schemas/tables/indexes/__init__.py | 26 +-
.../databases/schemas/tables/rules/__init__.py | 26 +-
.../tables/templates/foreign_key/sql/nodes.sql | 2 +-
.../databases/schemas/tables/triggers/__init__.py | 31 +-
.../servers/databases/schemas/types/__init__.py | 19 +-
.../servers/databases/schemas/views/__init__.py | 15 +-
.../databases/templates/databases/js/databases.js | 197 ++++++++---
.../servers/templates/servers/servers.js | 372 ++++++++++++++-------
.../templates/servers/sql/9.1_plus/stats.sql | 40 +--
.../templates/servers/sql/9.2_plus/stats.sql | 40 +--
.../browser/templates/browser/js/browser.js | 6 +-
.../browser/templates/browser/js/collection.js | 22 +-
.../browser/templates/browser/js/messages.js | 11 +-
web/pgadmin/browser/templates/browser/js/node.js | 63 +++-
web/pgadmin/misc/depends/static/js/depends.js | 32 +-
web/pgadmin/misc/sql/static/js/sql.js | 29 +-
.../misc/statistics/static/js/statistics.js | 29 +-
.../static/js/alertifyjs/pgadmin.defaults.js | 143 +++++++-
web/pgadmin/utils/ajax.py | 28 +-
web/pgadmin/utils/driver/psycopg2/__init__.py | 74 +++-
web/pgadmin/utils/exception.py | 42 +++
51 files changed, 1232 insertions(+), 967 deletions(-)