Improve handling of Lucene query parser errors

[joewiz]

Keyword searches that start with an asterisk trigger a stack trace, e.g., https://history.state.gov/search?q=*blah. We should catch Lucene query parser errors and report human-readable error messages:

We should probably surround our core queries with try-catch blocks. Ideally we will show the user a useful, actionable error message, but at the very least we should fail more gracefully than this.

See also @plutonik-a's observation in #89 (comment).