Fix off-by-some --height-limit bug

[casey]

Fixes #517. We were reading the height using self.height(), which opens a new read transaction, which will return the old height, until the current write transaction is committed.

Instead, read the height from the open write transaction, and increment it every time we index a block.

This should be ready to merge once I add a test.

todo:

• remove transactions from dummy blocks?
• #[rpc] -> #[jsonrpc_derive::rpc]
• consider parsing options directly
• do we need Default impls?
• fix localhost address
• convert height_limit to u64
• convert --height-limit integration test into unit test
• can i get rid of fallible conversion?
• make height stuff coherent
• reorder BicoinRpcServerHandle