look for invalid names for pubmed queries

Why was this change made?

Code changes for #1546

if an author has a name that includes "Or", "And", or "Not" (case insensitive, either first or last), that name will be ignored when constructing the query ... this means a user could in theory have a second "alternate identity" name that is valid, and we would still use it
if there are no valid names available, the entire query will be marked as invalid and thus not run, producing no results
while I was making this change, I extended our existing check for invalid names (currently only first name must have at least one character) to ensure the last name also has to have at least one valid character (eg. a last name of blank or null will also be marked as an invalid name)
reorganize spec to put all of the tests related to the valid? method in a describe block

Added new tests