Fixed validation error in bigboard config form

Closes #16 

Was expecting wrong validation response in L82 of bigboard-conf.lua.
Also cleaned up duplicate debugger import and log statements.

To test, 
1. Enable bigboard send (Advanced > BigBoard Configuration) and enter a hostname or IP address in the form field. The form should save with no errors.
2. Enter an invalid hostname/IP address. Save should reject with an error.
3. Disable bigboard and save, then re-enable. The form field should read "x.x.x.x"