General ISD Generation Fixes + Dawn Notebook (#206)

* Small import fixes to dawn

* More imports and updated the start_time to utc_start_time

* Added properties to dawn driver to get things working

* General changes to bring the isd back in line with isds generated in late April

* Update to dawn driver for detector sample and line center

* Added dawn notebook

* Fixed small type in sensor

* Fixed load/loads function

* Removed unnecessary print from load function

* Updated formatter test

* Updated load and loads to use a default formatter

* Minor import shuffling

* Reverted center ephemeris time

* Updated camera driver mixins to set the ephemeris stop time

* Suggested changes and test updates

* Removed weird driver importing

* Updated return in data_naif

* Small changes to get tests passing

* Updated line scan center ephemeris doc string

* Removed stop time from tests as it is computed from other properties