Create a seperate file for each table entry #25

The following structure should be reached:

- Table 0 (Folder)
    - Entry 0 (File)
    - Entry 1 (File)
    - Entry 2 (File)
    ...
- Table 1 (Folder)
    - Entry 0 (File)
    - Entry 1 (File)
    - Entry 2 (File)
    ...
...

Development branch: https://github.com/SimonG96/GBase/tree/ImproveDataHandling_%2325

FileHandler:

has pool of IDataHandlers
when no DataHandler is available the method that requested one has to wait
when a DataHandler is aquired the action can be executed
has to save all files
has to pass the correct file to the aquired DataHandler

DataHandler:

writer and reader won't have file opened all the time
needs ability to receive file handle to work with
has to be adapted to the "one file per entry" strategy