Measure and display time for three things during the Rails boot process

The goal of this change is to increase visibility of boot times, so each
developer can see when they increase. It might also improve the waiting time
by letting the developer know what happens during the waiting time.

Measured things:
* require 'rails/all'
* Bundler.require
* OpenProject::Application.initialize!
Merge pull request #258 from opf/feature/rails3_show_load_times

Measure and display time for three things during the Rails boot process