Support a MyMonero wallet adapter in addition to RPC and JNI

[woodser]

This issue requests support to manage a Monero wallet using a MyMonero-compatible server, which shares the wallet's view key with a third party in order to offload synchronization of incoming transfers.

The wallet should implement the MoneroWallet.java interface in order to conform with this library's wallet specification and be tested with existing tests.

[CryptoGrampy]

There is currently a 5 XMR bounty for this:

https://bounties.monero.social/posts/90/1-000m-implement-monero-light-wallet-server-client-library-for-android-native

[everoddandeven]

Hello

[woodser]

There is ongoing work to support a light wallet in this PR: woodser/monero-cpp#58