#601 Supply default subject line for journal entries

[Timothy Lord]

Right now, composing a journal entry without a subject line and hitting "preview" works to actually preview, but subsequently clicking Save generates an error because of the missing subject.

Parallel to "User Journal" being a provided default setting (no error generated if no other topic is chosen), it would be good to provide a default setting for the title as well, such as "Journal entry of April 29, 2009" or "UNIX TIME 1240560208."

This would avoid a frustrating error, and hopefully be amusing to the journal user.