Feature/432 live server logging

To test this, set DEBUG = False and insert a runtime error, for example insert a syntax error in akvo.rsr.views.project_list (starts at line 186 in views.py). This should result in the Error 500 page being shown when accessing http://rsr.akvo.org/ and there should be an error log record in /var/akvo/rsr/logs/akvo.error.log. The logging should not occur when DEBUG = False.