Naming of train/evaluate #168

This is admittedly some bike-sheding, but typically when programming with objects, method names (especially ones that change state) are verbs and attributes are nouns.

With train/eval mode we completely swapped this: the methods (training() evaluation()) are nouns and the attribute (self.train) is a verb.

We should fix this before release. Either:

• Use a python property and get rid of the methods
• Use verbs or abbreviations for the methods (i.e train() eval())