Move dbm class to own file.
Move layer class and subclasses to own file.
Fix authors.
Move inference procedure class and subclasses to own file.
Move sampling procedure class and subclasses to own file.
Fix missing import.
Add newline at the end of file.
Reorganize imports.

Move after authors.
Sort alphabetically.
Merge pull request #565 from herr-biber/refactor-dbm-file-structure

Refactor dbm file structure