Fix Exporting from GUI

The results saved from the GUI ignored "top X" and "threshold" settings, but
now they pay attention properly.
Minor Revisions to views/main.py

- removed unnecesssary comments
- made relative import absolute
- added method decorator for a PyQt slot
Revise "About" and "WorkflowManager" API Docs

Especially in adding better documentation of how to use the
WorkflowManager with len() and indexing and so on.

This also means that giving IndexedPiece objects to WorkflowManager is an
undocumented feature; I only left it because it's important for testing.
(cherry picked from commit 3248b796923f63f4cce710c4049fde14713cef49)
Further Improvements to WorkflowManager Docs; Remove _for_sc()

- Since we can't implement _for_sc() as a "modification," I removed it.
- Improved docs or other things.
(cherry picked from commit d537afeae9c0b18525950f36d760721ec500e0d3)
Changed "interval quality" and "simple intervals" to Shared Settings

- (in the WorkflowManager)
- also updated the documentation
- also updated the tests, including new tests to test_init_X() to ensure
  it also tests the shared settings are properly initialized
(cherry picked from commit 9347c154e19d126d9dc6b8851f24138b7522e961)