Convert some properties to auto-properties

Background
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This pull request is meant to reduce the changes required in [my other pull request](https://github.com/DynamoDS/Dynamo/pull/3193). The properties involved in this pull request do not really need setter or calls to ```RaisePropertyChanged``` (since they will never be set in the lifetime of Dynamo).

Notes to Reviewer
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Hi @ke-yu, please take a look. If it looks good to you and I'm not available when you get around to review it, please help me to merge it into ```master``` and cherry-pick it (the single commit) for ```Revit 2015```. Thanks in advance! :)