A little bit of refactoring

[tuomokar]

Some refactoring:

• bootstrap styles for error messages
• scripts now in their own file
• the template files are now divided into separate folders (references in templates/references and reference lists in templates/referencelists)
• removed some switch statements
• added comments for the controller methods
• added a couple of checks to the controllers (e.g. if a user tries to get into the reference creation page directly without choosing the type, they get redirected to the choosing page)
• when a reference list is exported to a bibtex file, it gets the list's name as its default name if a name isn't given otherwise

.. and some other general refactoring.

[coveralls]

Coverage decreased (-0.4%) to 94.553% when pulling e3c6b76 on tuomokar into 26db98a on master.