Tools: Introduce new "Upgrade Forums" tools section.

• Uses some awesome trickery to reuse as much of the "Repair Forums" API as possible
• Introduces a few new functions to handle the output of the new screen
• Removes hard-coded referencs to bbp-repair page, to allow usage on any relevant page (including new bbp-upgrade)
• Makes components & overhead lists smarter, and only includes items relevant to the current view

Fixes #3052.