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.
