Revert "Add modelID property to MIKMIDISystemExclusiveCommand"

This reverts commit b87648dc2f767918ee56776ce715debdbfc9afe3.
Resolve ambiguity with sysexData and sysexChannel

Add "universal" property to indicate whether sysex message is universal. These messages will contain a channel byte. Everything after that byte is considered sysexData - there's no change in the subdata that was getting returned prior to this change. In the even of a non-universal sysex message, channel will be 0, since channels aren't normally included in sysex messages, and sysexData will span a range starting with the byte following manufacturerID (prior to this change, that information was discarded).

That means: for universal messages subID's are included in sysexData, for non-universal messages, any device specific information (such as modelID, versionID or whatever manufactures decide to include) will be included in sysexData.
Make MIKMIDICommand descriptions easier on the eye

Add additionalCommandDescription method, which returns empty string by default, and gets overridden in subclasses to return command details. Move data dump onto next line