New UI, add status bar and sidebar, improve error handling

Segwit check, wait for chain header to download

added shutdown command for the full node to the UI's unload event

to close the underlying node, replaced the window.beforeunload event by an http request at electron level

Adding a keepalive endpoint that if enabled will shutdown the node after a trashold

Adding a shutdown api method

Rename smallestBlockHeightInWallet to earliestWalletHeight and added …

SyncManager now doesn't wait for the full chain to be downloaded but …

SyncManager now doesn't wait for the full chain to be downloaded but rather wait until we have enough data to start asking for blocks

Improve error handling

- Wait on API to load UI
- Add basic error handling to API calls