add test data for the retain strategy
fix: rows were not retained when specified as table-only rule

i. e. a rule "TABLENAME Retain PK='something'"
did not result in RetainStrategy.transform being called for
a row because the TableRuleMap was not queried for strategies
not applied to a column in Anonymizer#copyAndAnonymizeRow
UniformDistributionStrategy can now remove small categories

the syntax for the additional rule info is as in the following examples:
require minimum 2
require at least 2
require min 10%
SUBSTR(..., 1, 2); require at minimum 25
require at least 10 %; SUBSTR(..., 1, 2)

closes #9