[FIX] Starting conversion of insegt to new stream module.

* using new bam_io and gff_io modules for I/O
* manually generated GFF is using stream interface now

Note that the app tests are still broken.
[FIX] Actually opening the GFF file in insegt.

The remaining issue is now related to the output.
Merge pull request #38 from holtgrewe/feature/stream/adjust-insegt

[FIX] Starting conversion of insegt to new stream module.