Re-engineer the background process executor, to avoid using sqlite as some builds of
components it relies on do not support working in forked children.
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.
