[pgAdmin4][RM3136] Stabilise feature tests for continuous running on CI sytems

Hi Hackers,

Attached is the patch for feature tests, mostly fix issues due to which
test cases were failing on jenkins. It has the following fixes,

- Added code to Create testing db node from runtests.py with random
number in name to avoid naming conflicts in parallel execution on different
platforms.
- Added code to delete testing db node from runtest.py.
- Removed the code to add and delete testing db with name
"acceptacne_test_db" in each feature test cases.
- Added `setTestDbName` method in route.py module , through which
testing db name will be available for all feature tests.
- xpath/css selectors changes where applicable. Where it was possible I
have used css selectors.
- sqleditor.js - added the code to render
Explain Options submenue on left side on small screen.
- Increased the timeout for application from 60 to 90 seconds.
- Change the logic for reset layout funciton.

Last successful execution on all platfroms can be seen on following link

http://pgabf-jenkins.ox.uk.enterprisedb.com:8080/view/FeatureTest%20(Adhoc)

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Thanks,

Usman Muzaffar
QA Team
EnterpriseDB Corporation