feature: make elements in records addressable

[riedde]

E.g. works: sometimes it is necessary to refer to a certain aspect of a record (e.g. the second movement of a sonata, or 12th number of an opera).
I know that this will be a big feature, but I would like to thing about this.

I propose on data level something like <rs type="mdiv" target="workID#mdivID">. This seems very easy, but the bigger problem then is to update all ID-Patterns and checks on this and to introduce a second process level into the WebApp code.

For thinking about this we need an overview which areas of the WebApp would be impacted by working on this feature

[peterstadler]

related to #330