Unescape the descriptionfield of an event so HTML entities are decoded.

Ghost User
2017-10-03T16:20:34+02:00

Closes #491

#### Previous behaviour
Steps to reproduce:
1. Go to calendar and select month or week view.
2. When hovering over an event there are HTML entities in the description.

#### New behaviour
Steps to validate that it works:

1. Go to calendar and select month or week view.
2. Hover over an event, HTML characters like & should be visible.