New Plugin Architecture

• new plugin-concept: transport, signers, verifiers and rpc-handlers are now plugins. See https://in3.readthedocs.io/en/develop/api-c.html#plugins for details on the plugins-concept
• fixed possible verifiedhashes-inconsistency
• removed CMAKE-option ERR_MSG and combined it with LOGGING
• adding asserts in debug-mode
• optimize memory usage of all structs ( changing its order)
• change RPC-API which allows plugins to easily add custom rpc-methods.
• add cache-properties for custom cache entries withina request context
• add eth_sendTransactionAndWait which waitsuntil the tx is mined and returns the receipt instead.
• create request_signer as plugin, which allows multiple signers with different addresses
• added in3_init which should be called after loading in3 as a lib in order to register all default-plugins.
• fixed #18 (python transport issue for win)
• fixed wasm-issues in abi-handling - added optional timeout when waiting for tx receipts
• better error-messages in configure - add EWC-chain to dotnet and java bindings
• optimize cache write operation by only writing if changes exist
• fix wasm bug when reporting invalid responses after a client was disposed. (delaying free)