pgAdmin 4 commit: Added support different maintenance operations

Added support different maintenance operations
i.e. vacuum, analyze, reindex, cluster.

Tweaked by Ashesh for:
* Integrate it with the background process executor, and observer.
* Changed the UI for operation selection from select2 to custom radio
group.
* Made it consistent with other tools like backup, restore, etc.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=c34e62207a21b4f3e5a586e8e7d863f059bb9662
Author: Neel Patel <neel(dot)patel(at)enterprisedb(dot)com>

Modified Files
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web/pgadmin/tools/maintenance/__init__.py | 231 ++++++++++++++++
.../tools/maintenance/static/css/maintenance.css | 4 +
.../templates/maintenance/js/maintenance.js | 302 +++++++++++++++++++++
.../templates/maintenance/sql/command.sql | 12 +
4 files changed, 549 insertions(+)