Adding `Genelengths` type

[VinzentRisch]

Like described in #23, several normalization methods will be added to the plugin.
The FPKM and TPM methods both need information about the gene lengths.
This information can be extracted from the artifacts with type CARDAlleleAnnotation and CARDGeneAnnotation.
To ensure that feature tables from other sources can be normalized with these methods, a new type called Genelength has to be introduced.
The type will include one TSV file with two columns: One with the gene names and one with the corresponding gene lengths.
Additionally a transformer has to be introduced that converts CARDAlleleAnnotation and CARDGeneAnnotation to Genelength.

[VinzentRisch]

GeneLength will be added to q2-types as SequenceCharacteristics