[pgAdmin4][Patch] To fix the issues in Debugger module

Please find patch to fix the below issues,

1) Debugger page layout

RM#2512

2) To fix the issue when you user clicks on Stop button and gets connection lost error.

RM#2511

@Dave,

When we stop the debugger using pldbg_abort_target() function and try to start it again in the same connection, we are not able to do so because we do not get response from plugin(async query results shows busy status only), I think that is the reason why in pgAdmin3 we have disable all the buttons and release the connection if user clicks on stop button, For time being I have done the same in pgAdmin4 until we find the solution for this issue.  

Misc changes are for PEP-8.

Please review.