Add rescan to SDK

Adds an SDK command to perform the rescan devices action on a server. Updated the client page to add a rescan button for each connected client in the list. If the client is the primary target (either because it is an auto-connected local server or the only connected client when detection is disabled), the main rescan button on the UI should also send the rescan request to that server.

The new rescan button only shows up for supported servers (protocol version 5+) though 1.0rc1 uses incomplete version 5 and will show the button but not handle the rescan.

Fixes #2712 (closed)