removed data_panel option from BatchTransform.

- the underlying dequeue shouldn't be modified, so forwarding to the
user function is a bit misleading
- if we want to provide a dequeue we should consider another class
or an EventWindow decorator.
refining the batch transform interface:
  - removed use_panel
  - default for refresh_period is now 0
  - refresh_period will only affect the recreation of the datapanel
  - user's transform method is invoked on every call to batch transform
added checks for change in optional parameters to trigger transform
recalculation.
added tests to ensure:
    - repeated calls with the same data window do not update batch transform
    windows.
    - repeated calls with the same data and same supplemental parameters do
    not update batch transform results
    - repeated calls with the same data and different supplemental params
    do update batch transform results
incorporating feedback from @richafrank
Merge pull request #101 from quantopian/fix_1516

Fix 1516