179: Watch only tmp monero wallet r=da-kami a=da-kami
When initializing Monero wallet, try to open temporary wallet, if opening errors then try to create it. If creating errors then fail with message asking the user to configure the wallet RPC.
If opening / creation succeeds get the block_height to verify that connection to wallet works, then proceed to swap.
Note: RPC error handling is hacky, but I don't see the value of investing time into that at this point. The problem is, that we don't deal with the json rpc errors properly for calls were we don't serialize the result into an object (because the response is empty). Eventually we should switch to using https://github.com/thomaseizinger/rust-jsonrpc-client but that does not support parameters `by-name` yet, see: https://github.com/thomaseizinger/rust-jsonrpc-client/issues/20
Co-authored-by: Daniel Karzel <daniel@comit.network>