The tests for the detect-tokens controller were nearly all broken. They
have been fixed, and a few improvements were made to controller itself
to help with this.
* The core `detectNewTokens` method has been updated to be async, so
that the caller can know when the operation had completed.
* The part of the function that used `Web3` to check the token balances
has been split into a separate function, so that that part could be
stubbed out in tests. Eventually we should test this using `ganache`
instead, but this was an easier first step.
* The internal `tokenAddresses` array is now initialized on
construction, rather than upon the first Preferences controller update.
The `detectNewTokens` function would have previously failed if it ran
prior to this initialization, so it was failing if called before any
preferences state changes.
Additionally, the `detectTokenBalance` function was removed, as it was
no longer used.
The tests have been updated to ensure they're actually testing the
behavior they purport to be testing. I've simulated a test failure with
each one to check that it'd fail when it should. The preferences
controller instance was updated to set addresses correctly as well.
* Specify type before parameter name
Various JSDoc `@param` entries were specified as `name {type}` rather
than `{type} name`.
A couple of `@return` entries have been given types as well.
* Use JSDoc optional syntax rather than Closure syntax
* Use @returns rather than @return
* Use consistent built-in type capitalization
Primitive types are lower-case, and Object is upper-case.
* Separate param/return description with a dash
