storageFormats: Move hash class to own file.

Move the hashCalculator (renamed from md5Wrapper) to its own source and header
file so that it can be used more widely.
storageFormats: Rename variables.

As I have been informed that the variables names which have been chosen were
imprecise, rename the corresponding variables throughout the storageFormats'
source files.
storageFormats: Revise eventStorage.

Completely revise the eventStorage: there is now an eventStorage class which is
the only thing stored in the event files. With this implementation, hadd is
functional and the hadded files have valid hashes and concatenated users
strings. The eventFileWriter and the printMetadata executable have been adapted
to these new additions.

Unfortunately, the event tree is not saved as a pointer in the eventStorage
object, as there seem to be problems with saving the tree to disk in that case.
The impact of this as well as possible alternative solutions will be
investigated.
storageFormats: Remove names.

Remove all the arguments and variables dealing with the names of the root
objects saved in the event files, as this information is hard-coded in the
eventStorage class.