Stop using java.awt.Color

[HopeBaron]

Kord uses java.awt.Color to represent colors. This issue suggests moving to our own/a multiplatform implementation.

Why switch from java's implementation

• People using jlink to reduce the size of the JRE are forced to include the java.desktop module for what in our use case is a glorified integer. It comes down to ~30 megabytes which would be nice to shave off.
• We'll move to multiplatform eventually, and will be required to implement a Color regardless (or risk depending on an npm module!). We might as well make one that fits all platforms.

Isn't this outside of Kord's scope

It is, technically, outside of our scope. A color class is not related to the Discord API. A simple Color(r,g,b) should be sufficient though. The alternative would be to just accept an integer, which would be a dramatically worse user experience.

Issue originally made by @BartArys