[pgAdmin4][RM3136] Stabilise feature tests for continuous running onCI sytems

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.

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