Merge #13248: [gui] Make proxy icon from statusbar clickable

Summary:
6d5fcad576962e5950641f7e7b113a6ac6f397e5 [gui] Make proxy icon from statusbar clickable (Cristian Mircea Messel)

Pull request description:

Clicking on the proxy icon will open settings showing the network tab

https://github.com/bitcoin/bitcoin/pull/11491#issuecomment-336685303

Tree-SHA512: c3549749296918818694a371326d1a3b1075478918aaee940b5c7119a7e2cb991dcfda78f20d44d6d001157b9b82951f0d5157b17f4f0d1a0a242795efade036

Backport of Core PR13248
https://github.com/bitcoin/bitcoin/pull/13248/

Depends on D4269

Test Plan:

make check
./bitcoin-qt -proxy=<valid proxy>

Clicking the P icon in the bottom right corner should open up the network tab in the options menu.

Reviewers: deadalnix, Fabien, jasonbcox, O1 Bitcoin ABC, #bitcoin_abc

Reviewed By: deadalnix, Fabien, O1 Bitcoin ABC, #bitcoin_abc

Differential Revision: https://reviews.bitcoinabc.org/D4270