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.
Tweaked by Ashesh Vashi to integrate the backgroud process, and also
with some improvements as stated below:
* Resolved an issue loading existing preference.
* Improved the background process observer/executor for supporting
detalied view.
* Added the utility path preferences in the ServerType class.
operation like backup, restore, etc within it.
Also:
* improvised the color combination of the background process logger.
* Removed an unnecessary print statement from the
get_storage_directory(..) function, also return None if STORAGE_DIR
is set to None.
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.
