pgAdmin 4 commit: Adding a background process executor, and observer.

Adding a background process executor, and observer.

We will be using the external utilities like pg_dump, pg_dumpall,
pg_restore in background. pgAdmin 4 can be run as a CGI script, hence -
it is not good idea to run those utility in a controlled environment.
The process executor will run them in background, and we will execute
the process executor in detached mode.

Now that - the process executor runs in detached mode, we need an
observer, which will look at the status of the processes. It also reads
output, and error logs on demand.

Thanks - Surinder for helping in some of the UI changes.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=pgadmin4.git;a=commitdiff;h=f682f06c944004ee2386a2d75a65ed8e16683987

Modified Files
--------------
web/config.py | 2 +-
.../browser/templates/browser/js/messages.js | 4 +-
web/pgadmin/misc/bgprocess/__init__.py | 122 +++++
web/pgadmin/misc/bgprocess/process_executor.py | 375 ++++++++++++++++
web/pgadmin/misc/bgprocess/processes.py | 385 ++++++++++++++++
.../misc/bgprocess/static/css/bgprocess.css | 153 +++++++
web/pgadmin/misc/bgprocess/static/js/bgprocess.js | 500 +++++++++++++++++++++
web/pgadmin/misc/sql/__init__.py | 6 +-
web/pgadmin/model/__init__.py | 19 +
.../static/js/alertifyjs/pgadmin.defaults.js | 2 +-
web/setup.py | 19 +-
11 files changed, 1578 insertions(+), 9 deletions(-)