cubi-tk snappy itransfer-* LZ selection is faulty

[Nicolai-vKuegelgen]

Describe the bug
There appear to be 2 different issues with setting destination LZ in cubi-tk snappy itransfer-* commands

1. The destination argument is described as a project UUID or LZ-path by the hepl strings. However, giving a LZ-path does not actually work with those functions that try to read the snappy biomedsheet first.
2. cubi-tk tries to select from existing active landing zones. However, a delegate or owner may see LZs he does not own and can not write to. If these are lexicographically lower than ones own active LZ cubi-tk can not select them.

To Reproduce
Steps to reproduce the behavior:
for 1:

• try cubi-tk snappy itransfer-ngs-mapping <LZ-path>
  for 2:
• have a project where another user owns an older LZ and be delegate/owner
• try cubi-tk snappy itransfer-ngs-mapping <project UUID>

Expected behavior
Help string or function should be modified to match.
cubi-tk should filter LZs by user.