Sc204/alg in output

See merge request !115

Output files contain now an indication of the date and time in their name, making them unique, assuming no files are saved at the same second.

Added functionality that stores the last used algorithm, so that this can be recalled even though the user changes the algorithm after running a comparison.

Added str to AlignmentStrategies and subclasses so that those objects can be used to get a string to add to the filenames or anywhere else.

Created a more general function for the _center_view and implemented the changes in the view and splash.

Used a tk.StringVar() for the radiobuttons, so that it will work correctly in the future and it does not start as both selected.

Removed a few lines that could possibly break the program, because it called a non-existing function. The for-loop surrounding it would never be triggered anyway, so it could just be removed.

# Conflicts:
#	umbra/dutch_mmetaphone.py
#	umbra/tests/test_dwn.py
#	umbra/view.py

# Conflicts:
#   umbra/dutch_mmetaphone.py