[pgAdmin][RM5521] pgAdmin dump servers issue in desktop mode

Hi Hackers,

Attached is the patch to:

1) Fix an issue when dumping servers from a desktop pgAdmin app by providing an option --sqlite-path. This will allow the user to dump a specific config db file.

2) While there is an option for --sqlite-path now, the other paths for session, storage, etc. were failing with permission errors. Code is changed to not to bother those directories when dumping or loading servers.

3) Improved --help for setup.py.

4) Docs updated.

Please review.