removed combo box in TimeframeCorrelationView and added a textbox instead
caches are directly in (Timeframe-)FeatureCorrelationView
caches use Tuple<> instead of nested dictionaries
a control EnhancedStringConvertibleMatrix inherits from StringConvertibleMatrixView to reduce code duplication
add interface IDependencyCalculator to several calculators
fixed bug: a previous started calculation is cancelled, if a new calculation shall be started and the values are already in the cache
fixed bug: if the content is changed, the calculation is cancelled
HeatMap is still used for the dependency representation, because a class is needed which implements IStringConvertibleMatrix and it has a maximum and minimum value.