Fixed: IndexedPiece.get_data() Handles music21.stream.Stream Objects Correctly

We didn't properly re-import the piece for analyzers requiring Part or Score
objects. Now we do.

Closes #289
New: setting for FilterByOffsetIndexer

Now the 'method' argument can be changed. It's default is still 'ffill'.

Related to github issue #305
New: optional parameter in WorkflowManager._run_off_rep()

Added optional parameter called is_horizontal which changes the 'method'
setting in FilterByOffsetIndexer. If is_horizontal is set to True, method
will change to None. The default for is_horizontal is False.

Related to github issue #305.
Docs: in an example in offset.py

The example in offset.py lines 128-146 needed a minor edit to
incorporate a dissonance where the text description called
for one.

Closes #308 on github.
Fixed: horizontal interval calculations with FilterByOffsetIndexer

Horizontal intervals were incorrectly repeated when the lowest
voice was sustained longer than the offset interval. Fixed by setting
is_horizontal kwarg in the WorkflowManager.

Related to github issue #305
Tests: added integration test for previous FilterByOffsetIndexer bug

Tests proper calculation of horizontal intervals and adds a new piece
to the test corpus, Kyrie_short.krn.

Closes #305
CHANGE: default of 'continuer' to 'dynamic quality'

The previous default was for the 'continuer' to be set to label
unisons that arise from stationary lower voices with '_'. Now the
default is 'dynamic quality' which sets the label to 'P1' or '1'
depending on whether 'interval quality' is set to True or False
respectively. The user can still override it with a custom string.
Some tests were modified to accomodate this change.

Related to #309.
Tests: Erased redundant test in test_ngram.py.
Tests: renamed test_settings_0 to test_settings_9.
Fixed: continuer now returns to 'dynamic quality' when it should.

When the continuer was left to it's default of 'dynamic quality',
it would change to 'P1' or '1' after running an experiment. Now
that change still happens for experiments, but after each experiment
the continuer now gets reset to 'dynamic quality' if that's what
it's setting was before the experiment.

Related to #309.
Tests: unit tests for continuer setting functionality in test_workflow.py.

One test added and two tests modified. They verifiy that the user can pass
a custom string for the continuer setting and that the continuer setting
returns to 'dynamic quality' after running an experiment if that's what
it was set to before the experiment.

Related to #309.
Tests: unit and int. test fixes for continuer in test_workflow_integration.py

Verifies correct functionality of continuer when changed to a custom
string and also when left as 'dynamic quality' both with 'interval
quality' set to True and False.

Closes #309
Merge branch 'master' into devel_2 (manually modified)

Conflicts:
	vis/analyzers/indexers/offset.py
	vis/tests/test_offset.py
	vis/workflow.py

CRA: This took careful modifications to offset.py and test_offset.py because
they had both already been modified for vis-framework 2.x.
Formatting: Minor refactoring in offset.py