[pgadmin-hackers] [pgAdmin4][PATCH] SlickGrid result set format efficiency

PFA patch to reduce the size of query result set  by converting it into 2D array result set.

Additionally,

1) I had to change some logic in Debugger module to handle 2D array result set from async query (changes included in patch).

2) While testing I also found one issue where we are unable to right click on browser tree if we set Debug = False in config_local.py file, this was because of typo as path for css was changed to '/js/' to '/vendor/'.

(separate patch RM#2213)

Please review.