Removing restrictions to plotting with indels

Only 1 test case so far - needs much more work. But seems to work at
first glance.
Allow specifying GWAS catalog from command line

You can specify a GWAS catalog file now using --gwas-cat, rather than a
code for which catalog included in locuszoom you would like to use. The
codes still work as well (use locuszoom -h to view them.)