Change the TimelogController's to/from dates based on the project time entries

Instead of looking for the earliest and latest time entry system wide for the
dates in the form, now TimelogController will only look at the time entries
for the current project (and parent/sub projects).

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@4087 e93f8b46-1217-0410-a6f0-8f06a7374b81