milestone: Fix counting of open/closed issues.
issue: Remove caching which doesn't work correctly.
label: Make label works on any browser.
milestone: Calculate numbers just in time.

Milestone has stored many calcaulted values (e.g. number of open issues)
persistently in database and it causes many problems. They should be
calcultaed just in time.

Also remove many lines of codes because this fix eliminates the needs.
milestone: Fix a bug that state cannot be modified.