Fixup documentation

1. Adds the gwpy methods as the preferred way to set the strain data
2. Removes references to some of the problematic helper functions
3. Adds a bilby.gw.detector.Interferomer.set_strain_data_from_gwpy_timeseries wrapper for consistency
4. Various minor fixes to other documentation pages

changed milestone to %0.5.6

added Documentation label

approved this merge request

approved this merge request

merged

mentioned in commit 6075aa71