Better feedback to user

[rjchow]

Informational UX

1. show ledger nano connection status
2. show user's account balance
3. prompt user to confirm transaction in his wallet (both metamask and ledger)
4. cert store deployment status feedback
5. batch issuance transaction feedback
6. invalid input feedback (e.g not a hash or missing 0x)

Error flows

1. we can detect if contract data is enabled using https://github.com/LedgerHQ/ledgerjs/tree/master/packages/hw-app-eth#getappconfiguration
2. check if user has any ether
3. check if there's a document store at specified address
4. can check if the user has deployed any document stores previously using etherscan api, http://api.etherscan.io/api?module=account&action=txlist&address=0x007d40224f6562461633ccfbaffd359ebb2fc9ba&startblock=0&endblock=99999999&sort=asc&apikey=YourApiKeyToken

[thefiend]

Number 2 added in #95 .