station: add methods `copy()` and `is_active()` to BaseNode class
station objects: add .select() method (returning shallow copies)
bode plots: add option for time constraints
refactoring/docstrings
refactoring
minor bugfix
basemap plot: slight adjustments to "local" projection

- adjust axes for ticklabels
- adjust basemap region (width/height) to match figure aspect ratio
  (avoids squishy axes with large empty spaces around it)
basemap plot: colorbar option to force it on/off manually
Inventory/Network: Location preview plots + image tests