Improve -l option detection and add --center option to /dh h create command

[Andre601]

I've made some improvements towards the /dh h create command.

Namely, I've reworked how the plugin detects the -l:<world>:<x>:<y>:<z> option by not having it hard-coded in a particular part of the command, but by having it iterate through the args, finding it.
Should it not find it will it simply add the arg to a list to then use as the line content.

I also added a --center option, which when present will have the Hologram be centered, as if the /dh h center command was used.