Move towards using yaml instead of def config files

[johann-petrak]

This should allow to specify a number of additional useful properties for the list file, for example:

• use a tsv file with a header for fixed features or without a header to use generated feature names or feature names defined in the yaml file (Support TSV files as list files johann-petrak/gateplugin-StringAnnotation#8)
• Allow to specify an arbitrary list of feature values for each list file, in addition or instead of majorType/minorType/language (Better handling of list-specific features johann-petrak/gateplugin-StringAnnotation#6)
• Allow to specify types for features so that values get stored after type-specific conversion. This could then even work for simple structured types like lists

To simplify this, provide an easy converter from def to yaml, maybe.