Merge TokenDetectionController with DetectTokensController (from extension), and migrate to this repo

[mcmire]

These controllers are similar but have separate implementations. We will need to dive into how they are used in the extension vs. mobile app to understand what a combined version should look like.

While we are doing this, it may be worth it to complete the following items before completing the merge:

• Extract any API interactions or complex utility functions
• Refactor the detectTokens / detectNewTokens method (as it is quite complex): https://github.com/MetaMask/core/issues/1614
• Write comprehensive unit tests: https://github.com/MetaMask/core/issues/1615

Additionally, there are patches in mobile around TokenDetectionController under @metamask/assets-controllers, and we will want to make sure those are integrated as well.