Add Bed Filter Parameter and Close #48

[jylee-bcm]

This PR implemented as the guide of the Issues

$ nextflow run . --bed_filter /some/path
$ nextflow run . --exome_filter
$ nextflow run .

Tasks

• [x] Rename --no_filter_exonic to --exome_filter throughout the codebase
• [x] Add --bed_filter parameter to the script
• [x] Update the README