Re-work how Plugins' Settings are accessed

[Athanasius]

Another one from the "some users utilise a lot of Plugins" genre.

With a lot of plugins that have settings the way in which each gets its own tab on Settings can cause that window to get very wide for no good reason.

So, re-work how this is done to avoid the issue.

Suggestion:

Instead of a tab per plugin utilise the Plugins tab, which already lists loaded plugins, to have a Settings button per plugin that has such, with an additional pop-up window when clicked.

Some careful consideration will have to be given to how this interacts with the "prefs changed" functionality. I think it might be best to make the per-plugin Settings be model with respect to the main Settings window. That would mean you could only see and access one plugin's settings at a time... but that's only a little more work than clicking between the current tabs.

[vStone]

Perhaps as a bonus we can simply enable/disable plugins there without having to rename the folders.

[Athanasius]

Perhaps as a bonus we can simply enable/disable plugins there without having to rename the folders.

This comment is essentially a dupe of #261