style(rxApp): Change colors for pre-prod menu

Closes #538
feat(Environment): Better ways to check for a valid environment

This addes the following methods to Environment:

  * isPreProd
  * isLocal
  * isUnifiedPreProd
  * isUnified
  * isUnifiedProd

For instance, rather than calling `'local' === Environment.get().name`
you can just do `Environment.isLocal()`
chore(rxApp): Put preprod colours into variables
Merge pull request #549 from rackerlabs/EOD-155-pre-prod

style(rxApp): Change colours for pre-prod menu