v1.2.0: Workaround for inconsistent plugin loading.

There is an issue with plugin loading order when a relatively large amount of plugins is loaded, causing plugins such as IAxPresenceFootsteps to load before ItemsAdder, even when the plugin is defined as a softdependency.

This update adds a workaround by making the entire startup procedure (checking for ItemsAdder, adding commands, etc.) run after the server is done loading.
This should hopefully fix issues such as #1 until Spigot and/or PaperMC implement a proper fix.

Read more here: PaperMC/Paper#5992