during construction so that the default JmeContext timer
could potentially still be used by calling app.setTimer(null)
from an apps main(). In that case, the previous behavior
of pulling the timer from JmeContext during init would happen.
git-svn-id: https://jmonkeyengine.googlecode.com/svn/trunk@8588 75d07b2b-3a1a-0410-a2c5-0572b91ccdca