renaming of assertion fields

[ahwagner]

We had a discussion during the documentation sprint today about the use of the terms summary (e.g. variant summary, gene summary) and statement (e.g. evidence statement) in CIViC. Assertions currently have a summary with an associated description, but we discussed that labeling the summary field as a statement is more aligned with the principle of assertions and the intent of the field.

We also discussed how the description field is typically the aggregated details of how the summary (statement) was generated, and thus may benefit from a field label of details.

@kkrysiak @obigriffith @malachig @ebarnell and @arpaddanos, your input here would be helpful as we strive to align the terms we use across these concepts.