[pgAdmin][RM2172] Search Objects Functionality

Hi Hackers,

Attached is the patch to implement search objects functionality in pgadmin.
The feature will allow a user to search for any object in a database.
Highlights of the feature:
1) Search any object with user input text with at least 3 characters.
2) Search can be done on a specific object type by selecting from the types
dropdown.
3) The search results grid will show object name, object type and the
object path on the browser tree. On double clicking the record, it will
locate that object on the browser tree. The columns object name and type
are sortable.
4) The object nodes which are disabled (hidden) using preferences will not
be visible in the types dropdown. However, in the case of all types, the
search records will be visible for those types greyed out.
5) You can also access search objects dialog using the button on the
browser toolbar.

Python and JS test cases added. Docs updated.
Please review.

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Thanks and Regards,
Aditya Toshniwal
pgAdmin Hacker | Sr. Software Engineer | EnterpriseDB India | Pune
"Don't Complain about Heat, Plant a TREE"