Add ability to disable dynamicFinders and associationFinders

- resolves #592
modified:   lib/waterline/query/finders/dynamicFinders.js
- only generate dynamic finders and association finders if the
  dynamicFinders and associationFinders flags are not false

modified:   test/unit/query/query.dynamicFinders.js
- unit test ability to enable/disable dynamicFinders and
  associationFinders