Improve data selection tools

[steob92]

The current data selection tools for when finding appropriate background files aren't fully implemented.

ToDo:

• [ ] Implement all search features (el, az, etc)
• [x] Implement stopping feature when finding backgrounds (e.g. take 10 closest hours)
• [ ] Implement custom region exclusions
• [ ] Implement custom source/run exclusion
• [ ] Implement search boundary extension

Some work needed to investigate how fuzzy search boundaries can be.