[Core] Make sure SOPluginLoader is non-copyable.
[Core] Better code.
[Core] Unload plugins on release.
[Core] Clear loaders.
[Core] Explicitly delete the instance object when unloading.

This also fixes numerous crashes on Qt5 on exit.
[BT] No need to keep some vars in auto_ptrs.
[Blogique] Parentless blogging platforms.

Fixes crash on release.
[Azoth Sarin] Remove accounts on Tox proto destruction.
[Azoth Murm] Remove accounts on protocol destruction.