tuc2014.urls: Add a better exception if crispy_forms was not found

Normally we don't require crispy_forms, but the language picker
uses it. Make this clear through a better exception message.
9 jobs for master in 25 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #87039
py27-django110

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py27-django111

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py27-django18

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py36-django110

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py36-django111

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py36-django18

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py36-django20

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py36-django21

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py36-django22

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