* Give each network the ability to specify default estimates, and whether or not they should fetch estimates from API. Convert gas slider to always use estimates.
* Fix gas cache invalidation, invalid too high / low logic.
* Fix up tests.
* tscheck
* Setup api / reducers / actions for gas.
* Implement gas price saga, fetch from component, and loading states. Blocked on CORS.
* Implement caching mechanism.
* Add tests for gas saga and reducer.
* More testing.
* Indicate that gas price is recommended when fetched from API.
* Hide track while loading.
* Fix tscheck.
* Check gas estimate before assuming its ok.
* Check for correct logical order of gas prices.
* Tscheck fixes.
* add gas limit/price constants
* add gas limit/price validators & selectors
* apply new gas limit/price validation to components and sagas
* create/apply function to sanitize advanced fields input
* add types, update tests
* fix unrelated failing test
William O'Beirne
Danny Skubak