formatting changes
add loading progress indicator since planning page can take a little while to load
add docblock type hint for swimlanes
disable epics list until it is loaded
only initially load issues for visible milestones in planning mode
hide backlog until it's done loading
show dropdown menu on whiteboard issues
only update milestone issues in loaded issue lists
removed old, unused code
include initial milestone counts for hidden milestones
allow assigning issues to milestones that doesn't have milestone issues loaded
improvements to planning loading progress indicator
minor refactoring for status distribution counts