Account for conflicting plugin names

[tal5]

Reported on Discord.

Addtions

• Depenizen.BridgeData record - just holds a bridge supplier & the new class checks.
• new registerBridge overload that takes a classCheck.

Changes

• allBridges now stores the new BridgeData, and all relevant methods take/pass it.
• bridgeData.classCheck is now checked in loadBridge if it exists, and stops loading the bridge if the class isn't found.
• The Quests bridge now has a class check of me.pikamug.quests.Quests.

[mcmonkey4eva]

I don't know if I agree with this check - there should be an error here, a plugin registered itself with the same name as a pre-existing decently well known plugin, that is obviously erroneous behavior.
It should be a big shiny red error, telling you somebody fucked up, because they absolutely did.
That said, the original discord report had like 5 duplicate stack traces in a row, and that's a bit excessive. It should just be one clear error, not a cascade. A shiny red glare in the startup logs, not a clusterfuck.