Improve the errors in all controllers

[mconf-daileon]

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Author Name: Leonardo Daronco (Leonardo Daronco)
Original Redmine Issue: 552, http://dev.mconf.org/redmine/issues/552
Original Date: 2013-01-29

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Most of the errors shown to the user are a bit too generic and do not really show what happened. In some circumstances the errors should be generic, but the specific error should at least be logged.

So all errors in the controllers should be reviewed and the logger should be used a lot more in controllers and models.