Zecwallet Light CLI: Bug fix release

This release of Zecwallet Lite CLI and SDK features several small improvements and bug fixes.

• Add unconfirmed_zbalance to reflect ZEC that has been received, but we don't have enough confirmations yet
• Add spendable to outputs, indicating whether the note is spendable yet.
• Handle the case where failure to broadcast Tx would still end up in the mempool
• Prevent syncing while Tx are being constructed
• Allow sending hex encoded memos to allow non-text memos.
• Accept a JSON encoded string to importing keys