Consider making certain instance variables read-only properties

[StokesMIDE]

Various classes in dataset.py use variables for things that shouldn't be changed by the user; changing them will either have no effect or a bad one. For example, EventArray has .parent, .dataset, .session, .hasSubchannels, .hasMinMeanMax, .allowMeanRemoval, .channelId, .subchannelId, etc. I was going to list everything, but probably the majority of instance variables of classes in dataset.py should be read-only; it would be shorter to list the ones that shouldn't.

In most cases, this would be a matter of something like renaming the variable with an underscore prefix and a property with the old name would just return that. Some internal changes would also be made so the class could access the underscore variable directly, saving an unnecessary function call.