softdepend on non-essential plugins and handle presence at runtime.

[Owen3H]

Right now, we hard depend on a lot of plugins via plugin.yml which means the whole API fails if just one of these fails.
This would make endpoint errors contained only to the presence of the plugin they are related to.

In the case of SuperbVote for example, the API was down for multiple days when most endpoints could have continued operating. However, this could also apply to the DiscordSRV or even Quarters plugins if they happen to fail in future.

[Owen3H]

I think error handling in general needs slight improvement.
Applying logic found in 0cb78ec to more endpoints would be a good start.

[Warriorrrr]

True, this isn't the first time the API has gone offline due to a missing dependency so it's worth improving. Would also make it easy for anyone wanting to contribute to test their changes without compiling our own version of superbvote and installing discordsrv/quarters.