fix: improved clonality event definition, usage of major subclone for assembly polishing; upgrade to varlociraptor 6.0

[johanneskoester]

Important: Before, we used only clonal variants (VAF=100%) for assembly polishing. This PR changes this behavior to also use major subclonal variants to polish the assembly (VAF>=50%). This is open for discussion. My idea is: the assembly should represent the major subclone in the sample (if there are multiple ones). If we only use clonal variants like before, the assembly could contain individual loci where the majority of the reads disagree with the assembly. This is not what we would want I think, since it also hampers the predictions of pangolin.

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