EXP-168. Normalize naming of Avro Classes.

The names of Avro records for columns and filters have been changed from
'*Spec' style to 'Avro*' to match other classes and distinguish
from records like 'AvroInputSpec' (which legitimately should end in 'Spec').

issue: https://jira.kiji.org/browse/EXP-168
review: https://review.kiji.org/r/975