Change cost to fine and add minimum fine

Changes "cost" field of events into "fine", to solve confusion regarding this.
Also places a minimum of 5 (euros) on the fine field, as is policy by the current board.

website/events/migrations/0013_auto_20170215_1950.py → website/events/migrations/0013_auto_20170215_2113.py

 # -*- coding: utf-8 -*-
-# Generated by Django 1.10.3 on 2017-02-15 18:50
+# Generated by Django 1.10.3 on 2017-02-15 20:13
 from __future__ import unicode_literals
 
 import django.core.validators
@@ -20,6 +20,6 @@ class Migration(migrations.Migration):
         migrations.AddField(
             model_name='event',
             name='fine',
-            field=models.DecimalField(decimal_places=2, default=0, help_text='Actual cost of event per participant.', max_digits=5, validators=[django.core.validators.MinValueValidator(0)], verbose_name='fine'),
+            field=models.DecimalField(decimal_places=2, default=0, help_text='Fine if participant does not show up (at least €5).', max_digits=5, validators=[django.core.validators.MinValueValidator(5)], verbose_name='fine'),
         ),
     ]