Allow more fine grained selection of projects and sorting

Work on #75 

Done:
 * Added possibility to filter subsets of projects in sprintly and github, and choose display order in feature list

Pending:
 * Tests
 * Maybe rethink the sorting criteria in feature list: currently they are sorted by provider, and within provider there is some implicit sorting. It may be that I want to list first PRs and stories from given repos (intertwined providers) or by priority within repos... I may create a proper story for this