added custom potions support

[robzen]

example: //adds a custom slowness potion with power 1 and 10 seconds duration to slot 0 '0' : '373:1:16426:slow:1:10'

[lol768]

Before I pull this, can you:

• Ensure all code is formatted with K&R brace style
• Ensure if and else statements have braces even if they only have one line of code beneath them

Thanks for your contribution!

[robzen]

no problem :)