[pgAdmin4][Debugger]: Initial Patch

Hi,

Please find attached debugger v1 patch. To test this patch we need to apply
the "function" module patch submitted by Khushboo.

For the debugger functionality, direct and indirect debugging is working as
per pgadmin3 except below TODOs.

Below are the TODOs which will be submitted in next patch along with the
fixed review comments.

- For the direct debugging, 'NULL' and 'Expression' column value should
be validated before pressing the debug button.
- User can deposit the value of input arguments and local variable but
need to be
validated against respective data types.
- Currently we have tested for plpgsql functions only, We need to test
against EDB SPL functions and trigger functions.
- For the direct debugging, once the execution is completed, only
"Continue/Restart" button will be enabled and user should allow to restart
the debugging with same function and previous values.
- Values entered by the user in input dialog during direct debugging
should be saved.

Currently we have tested this patch with PostgreSQL v9.5.

Do review it and let us know for the comments.

Thanks,
Neel Patel