Fixed E_NOTICE errors
Silencing additional E_NOTICE errors
Rewrote import process page & added IPv6 import support.

Have rewritten the import processing page - two biggest changes are adding in
IPv6 PTR zone support, as well as ripping out all the old input validation code
and replacing with the use of the shared validate_custom_records code.

Testing has been completed with a number of different Bind zonefiles, but
thanks to the wonderful range of different style Bind zonefiles, there's always
the possibility that this could introduce some new bugs till the teething
period is over.