Urls removed from emails + post deletion bugfix

This release has two things:

1. A bugfix by https://github.com/vojnovski, fixes an error when deleting posts in the web interface.
2. Removed the links to the page in the daily emails. This all of a sudden started causing the emails to be silently discarded by App Engine, without reporting any kind of errors. I only found this out by trial and error, and it's definitely the links causing it. So, now you just have to remember your url!

While doing this I added a couple of convenience things to the /sendmail handler.

• /sendmail?force=1 will send the email for the current day, no matter if it's been sent before. Useful for testing
• /sendmail?force=1&date=2016-02-01 will send the daily email for a specific date.