Context to include planetary and spacecraft constants

[ChristopherRabotin]

One of the most frustrating things with BSPs is that planetary constants are separate from the rest of the file. One needs to load the PCK (planetary constant kernels). The advantage is the simplicity in quickly changing planetary constants ... but that is rarely done in analysis. Moreover, gravity fields or gravity clones are completely separate and are found on NASA PDS instead of NAIF. This adds to the complexity of finding relevant information.

Objectives

• Context should include planetary constants #91
• Context should include gravity fields #89
• Context should include spacecraft constants #90