Ignore and delete old versions when copying plugins

[hlxid]

Description

When the version of a plugin is bumped it will exist twice in the plugins directory because the file with the old version number will still be in the plugins directory. ChatOverflow will load both versions and use the one first loaded which mostly the old version because it is loaded alphabetically and people will wonder why their changes won't take effect.

If people still copy an old version manually into the directory in e.g. the end-user deployment the framework should always use the newer version and warn that there are two versions installed.

How to reproduce

1. Have a plugin and starting ChatOverflow to copy it to the plugin directory.
2. Bump the version and restart ChatOverflow to copy the new version
3. The old plugin is still in the plugins directory and will still be used.

Refrences

@derNiklaas suffering from this on discord.