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!

Examples:
```
$ bundle exec rspec spec/models/user_spec.rb 
require 'rails/all'... 0.850s
Bundler.require... 3.240s
Application.initialize!... 6.120s
.................

Finished in 3.53 seconds
17 examples, 0 failures

Randomized with seed 23695
```

```
$ bundle exec rails server
require 'rails/all'... 0.740s
Bundler.require... 4.030s
=> Booting Thin
=> Rails 3.2.13 application starting in development on http://0.0.0.0:3000
=> Call with -d to detach
=> Ctrl-C to shutdown server
Application.initialize!... 3.960s
>> Thin web server (v1.5.1 codename Straight Razor)
>> Maximum connections set to 1024
>> Listening on 0.0.0.0:3000, CTRL+C to stop
```

```
$ cuke features/users/random_password_assignment.feature 
require 'rails/all'... 0.840s
Bundler.require... 3.920s
Application.initialize!... 3.980s
ruby -S bundle exec cucumber -r features features/users/random_password_assignment.feature
require 'rails/all'... 0.520s
Bundler.require... 3.290s
Application.initialize!... 6.380s
Using the default profile...
Feature: User Status

  Background: ...
```
(yes, cukes load everything two times, we should improve this)