Custom notifications

This release features custom notifications a dapp can trigger at any time by calling the new notify() method. Also included is a change to the API for onboard(), which now returns the current state object instead of a string with the last onboard step. This will help dapps with their post-onboard logic. Finally, Assist styling can be updated after initialization with the new updateStyle() method.

• API change for onboard() return value.
• custom notifications via notify() API. See docs at https://github.com/blocknative/assist/blob/master/README.md#notifytype-message-options
• new updateStyle() API to change style settings after Assist is initialized. See docs at https://github.com/blocknative/assist/blob/master/README.md#updatestylestyle
• fix for automatically scrolling to bottom of notifications container so new notifications are seen
• fix for contract delegation for web3 >1.0.0-beta.37
• added more tests for contract decoration