Duplicate Edition IDs In Use on Release Center

Instead of showing edition builds under "Project Releases" and "Edition
Releases", this commit only shows them under the appropriate Edition
section.  This prevents the issue of having duplicate IDs on the page.

This commit also fixes a bug where TBGBuild::isEditionBuild() was
incorrectly identifying builds as being associated with an addition.
The edition ID was 0 instead of null.

Finally, some of the markup was modified so that when the final build
was removed from any section, the muted text informing the user that
there are no releases for the project / edition is restored.

This issue fixes #2459
Merge pull request #317 from keelerm84/feature/2459-duplicate-edition-ids

Duplicate Edition IDs In Use on Release Center
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