Confirm with user before creating a new database or collection on mongo

IGV-2020
Give better error message when genome can't be downloaded (give full path)
Add ability to query features by name. No automatic index creation for that field, it may not be super-efficient

IGV-2020
Lookup feature by token instead of whole search string in SearchCommand (that was probably an oversight)

Add API hook for adding feature searcher. Not used yet, planning on implementing for Mongo
Save setting for Filter Secondary Alignments as set in preferences