Make rules independent of snakemakelib package

[percyfal]

It should be possible to include rules without making use of snakemakelib functionality. We can still set configuration defaults, but they should be general enough to be included without installing snakemakelib (for instance as url). This could be solved by doing conditional imports, and doing the bulk imports in the top-level settings rules, which is included by all files.

[percyfal]

This will be tricky for the function generic_target_generator. Affected rules are

snakemakelib/rules/bio/ngs/qc/rseqc/rseqc_qc_8_summary.rule snakemakelib/rules/bio/ngs/qc/cutadapt/cutadapt_qc_summary.rule snakemakelib/rules/bio/ngs/qc/picard/picard_merge_sam.rule snakemakelib/rules/bio/ngs/qc/picard/picard_do_summary.rule snakemakelib/rules/bio/ngs/qc/qualimap/qualimap_collect_results.rule snakemakelib/rules/bio/ngs/rnaseq/rsem/rsem_summarize_expression_data.rule snakemakelib/rules/bio/ngs/align/star/star_summarize_alignment_runs.rule