SE-219: Debug rendering home page with default configuration

The home page now renders something without throwing any errors. Added
missing includes to webapp's default templates. Expanded catching of Solr
errors to swallow them as intended.
SE-219: Return empty string for URL missing from JournalConfig

Returning an empty string was already coded if the JournalConfig object was
missing entirely, so it makes sense to return the same for a present
JournalConfig with an uninitialized URL. This loosens requirements for
journal.xml.