admin: Fix typos in admin tests
admin: Fix typo in deleted entries tooltip

Remove the "None." string that appeared on every category (besides
projects) due to a bad template tag. Also, add the tooltip in a
separate html file for easier editing.

Fixes apyrgio/synnefo#288
astakosclient: Create exception 'ConnectionError'

When astakosclient fails to connect to the remote server, raise a
'ConnectionError'. This exception contains the original Exception
thrown by httplib so that it can be used by other clients such as kamaki.