Replace EuiColorPicker with an accessible, custom component

[snide]

Fixes #853
Fixes #791
Fixes #790
Fixes #789

Replaces EuiColorPicker with a simpler system for color selection. The previous version was a simple wrapper around react-color so this removes that dependency.

TODO

• Write some tests
• Do a screen reader pass
• Update docs for every variation (compressed, disabled...etc)
• Make a swatchOnly version where you don't want to allow a hex input
• Provide a null / transparent state
• Add extraAction props for swatches and the input to allow + / - from the list if needed (canvas request)

[snide]

Speaking with @w33ble, canvas wants some extraAction props and example code to extend it like so. Added it to my todo.

[snide]

@thompsongl Were you forking this? Any reason to keep it up as a PR? Otherwise I'll close it out.

[thompsongl]

We can close this. Any work I do that builds on this can cherry-pick.