Add comments/definitions to all classes and object properties

[KonradHoeffner]

• [x] KH: Definition von SoftwareProduct zu HITO hinzufügen: "A software product is an acquired or self-developed piece of software that can be installed on a computer system." (auch Blaues Buch?)
• [x] KH: Definition zu HITO Feature hinzufügen: "Features are functionalities offered by the software product of the application system which directly contribute to the fulfilment of one or more function. The finer the granularity of an function is formulated, the greater is the probability that the function semantically corresponds with a feature an application component offers." (Quelle: Blaues Buch 2011)
• [x] merge with https://docs.google.com/document/d/1u-kJwPbJMqoLbJFybO6bcjkLdqKcoPmB_M7iM-uNPl4/edit# (done for #83)