In MainPanel:ResetTitle() - Changed to use SetFormattedText() to help curb garbage-generation.

In MainPanel:ResetTitle() - Changed to use SetFormattedText() to help curb garbage-generation.
In Player:SetProfessions() - Explicitly check for false, since a nil table entry will set spell names we don't care about.
When generating a new entry for the ScrollFrame list, set its is_header member to true if it actually is a header, otherwise ignore it - nil > false
Changed DEBUG() to addon:DEBUG().
Made miscellaneous syntax changes and variable/member renames for clarity.