New frontend look, bugfixes & code cleanup

[rafaelklaessen]

Frontend

• New login/account/reset password page look
• Removed unnecessary files
• Reorganized files (CSS in CSS folder, JS in JS folder)
• Used HTML5 & cleaned up JS
• Fixed ResetPassword.jsp showing a blank page when the resetId is invalid or already used

Backend

• JSON responses now have a response type of application/json instead of plaintext
• Improved error messages in error responses
• Made error & success responses JSON
• Fixed account bug (see Account fix #1)
• Fixed /oauth/account/createAccount not validating email address
• Fixed ApplicationRegistry not checking wether a client_id was already taken (similar to account bug)
• Fixed /oauth/auth not verifying redirect_uri which could cause a URISyntaxException
• Fixed NullPointerException in /oauth/resource_query when given access token was present but invalid
• Removed test code
• Cleaned up code
• Updated license year

[rafaelklaessen]

Please note that if this PR gets merged #1 isn't required anynore.