Fixes for issues #7, #9 and #12, and OnGather hook.

UI changes for https://github.com/RustOxide/Oxide-2-Patcher/issues/9
Code change for https://github.com/RustOxide/Oxide-2-Patcher/issues/7
Code change for https://github.com/RustOxide/Oxide-2-Patcher/issues/12
New hook, OnGather.

Syntax: OnGather( ResourceDispenser source, BaseEntity player, ItemAmount item )