Update method for `fwspp` object

[adamdsmith]

Store as an attribute the datetime a query was initiated. Subsequently use this to pass to the get_* functions to, I suspect, profoundly reduce the size and increase the speed of query updates.

• [ ] GBIF API accepts a lastInterpreted parameter
• [x] No obvious solution in BISON SOLR API
• [ ] Maybe datemodified in iDigBio API, but need to check further
• [ ] Perhaps lastindexed is appropriate VertNet parameter?
• [ ] No obvious EcoEngine solution, but probably not a huge concern
• [ ] No obvious AntWeb solution, but likely not a concern

[mccrea-cobb]

No longer needed for BISON.