[pgAdmin4][patch] Changes to stabilise feature tests

Hi Hackers,

Attached is the patch to stabilise feature tests. Major changes includes:

1) Changes required for working with Bootstrap 4.

2) Change to fix the timeout exception when waiting for element (tested multiple times on multiple server, did not occur to me thereafter)

3) Removed reset layout after each test case. Instead, delete the layout entry from sqlite db file and do a plain refresh. This will save some time and will also remove dependency on reset layout menu.

4) Disables tree state saving when feature test run starts. Feature tests got confused with auto expanding tree.