Add server tax functionality.

[KamosRZ]

Hello, since I needed this, I added a server tax functionality. I decided to share my changes just in case you need them someday - you don't have to accept the PR. I tried to follow your coding style but it's not exactly the same :D

The server tax can be defined in the config as a double between 0 and 1 and it represents what % of the price should be taken from the server before paying the seller.

[KamosRZ]

Alright, I pushed a couple of changes - optimise the code and show the message I am using on my server to show the buyer why he gets a little less money and why I added all those new placeholders.

Again, I did this for my server and just wanted to share so It's perfectly ok with me to discard those changes and make them yourself I won't feel bad :D

I also want to thank you for your plugin - It is literary everything I was looking for, for weeks.

[OliverP98]

Hey. I am extremly interested in this aspect of the plugin going into the next version, and I have looked around to see how I can implement it. I am not great at understanding what is happening on GitHub.

When would this be pushed to the main branch and onto the spigot page?

Thanks for the great work on the plugin!

[EpiCanard]

Hello @OliverP98,

I'm not planning a new release soon. So if you want this feature you can ask to @KamosRZ if he can give you a runnable jar of his version.

[EpiCanard]

Thanks for your work ! I will merge what you have done and rework it a little.