Better error messages for feeds #229

Right now I've got a lot of failing feeds and I don't know why.

As the error reporting is pretty sparse (Error parsing) it's hard to figure out what went wrong (on my side or a broken feed). Looking through each feed is burdensome.

If the error would be logged correctly it would be much easier (it does not really need to be shown in the web interface, if it can be found in heroku logs I'm fine with it)