Improved error reporting

Error mails now look like this:

~~~
App:                skylines.frontend
Time:               2013-12-08 15:06:47,820
URL:                https://www.skylines-project.org/about/license
IP:                 37.201.227.153
User:               Tobias Bieniek <tobias.bieniek@gmx.de>

Message:

Exception on /about/license [GET]
Traceback (most recent call last):
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1817, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1477, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1381, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1475, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python2.7/dist-packages/flask/app.py", line 1461, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/opt/skylines/src/skylines/frontend/views/about.py", line 47, in license
    l
NameError: global name 'l' is not defined
~~~