Add new isatab template 'cancer'

[sellth]

Discussed this with @mbenary. Current templates tumor_normal_dna & *_triplets are unsatisfactory in multiple ways, not the least by relying on external config injection for "triplets": https://github.com/bihealth/cubi-isa-templates/blob/89d1a026b7bbe7e7bfbdf449bd9a41696865a0d9/cubi_isa_templates/__init__.py#L108

We therefore decided to start a better named and hopefully more useful singular cancer template.

To do

• [x] copy tumor_normal_triplets files as a basis
• [x] adapt is_triplet logic to selectively add transcriptomics assay within the template
• [x] add human readable prompts
• [x] get feedback from @mbenary & @ericblanc20,
• [x] discuss addtional changes (i. e. removing not used protocol parameters)
• [x] remove tumornormal* templates?