Account for LOGMSG, EXECPAUSE and EXECACK messages in parser

[michaelosthege]

• LOGMSG are ignored, because every received message is logged already
• EXECACK and EXECPAUSE are handled like EXECEND: One may subscribe the category, but detailed information and association with the command message is not available.

Closes #34

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I noticed that EXECERROR → _parse_execerror results in a {"answer": "EXECEND", ... dict, leading to a potential conflict with EXECEND messages.
This is likely because the rest of the codebase only subscribes to EXECEND, never to EXECERROR.

I think one clean solution would be to include the command msg_id and aggregate not only one, but many responses per msg_id.

This would also account for the multiple EXECACK messages incoming during a multi-step program execution (if I understood that correctly).

Furthermore it would provide means to aggregate further details like cmdNr, progNr, programName in a sequence of typed response message objects.

In another project I use a similar pattern with MQTT communication, where every command has a "conversation_id" that's included in all response messages of different types.