Add GetBalance to CoinView

[quantumagi]

Merge PR #110 first.

Implements a very fast IEnumerable<(uint height, long satoshis)> GetBalance(TxDestination txDestination);

The first enumeration value comes from the Balance table and subsequent values are adjusted via the BalanceAdjustment table.

Only a fraction of a second (~40 ms) response time was observed to return ~1800 balance adjustments all the way to genesis.

Implemented ONCE in Coindb<T> which replaces LevelDbCoindb and RocksDbCoindb.

The code deals with the following issues:

• Keeping track of the height up to which balances are indexed so that address indexing can be toggled on/off without resulting in gaps.
• Replacing AddressIndexer with AddressIndexerCV and respecting the -addressindex setting.
• Adding missing XML comments.
• Adding the IDb compliant wrapper classes RocksDb and LevelDb.

/// <summary>
/// Returns a combination of (height, satoshis) values with the cumulative balance up to the corresponding height.
/// </summary>
/// <param name="txDestination">The destination value derived from the address being queried.</param>
/// <returns>A combination of (height, satoshis) values with the cumulative balance up to the corresponding height.</returns>
/// <remarks>Balance updates (even when nett 0) are delivered for every height at which transactions for the address had been recorded 
/// and as such the returned heights can be used in conjunction with the block store to discover all related transactions.</remarks>
IEnumerable<(uint height, long satoshis)> GetBalance(TxDestination txDestination);

Instead of adding migration code the coin database is automatically truncated and re-built (+- 5 minutes).

[quantumagi]

Still testing.

[quantumagi]

Bug fix - the table prefix is missing here and the bytes should be in big endian order.

[fassadlr]

Hi Gustav, release 1.3 will go out tomorrow as we are already in RC with the masternodes. Can you please point this to

https://github.com/stratisproject/StratisFullNode/tree/release/1.3.1.0

[quantumagi]

See #1031