Refactor gwpy.astro to depend on inspiral-range

Created by: alurban

This PR fixes #1248 (closed) by refactoring the gwpy.astro submodule so that it depends on the new inspiral-range Python package. As a result, the inspiral_range and inspiral_range_psd methods now fully account for cosmological corrections, while the SenseMon method has been refactored into corresponding functions sensemon_range and sensemon_range_psd.

Things to note:

• The inspiral-range package does not (appear to) support sensitivity metrics based on transient burst sources, so that functionality remains untouched
• Where possible, I have tried to include references to the inspiral-range package as well as the paper (Belczynski et al. 2014) that lays out the cosmology-corrected range calculation
• This PR also includes a number of smaller changes that do not affect overall functionality

Closes #1292 (closed).