Add batch processing/import

[Kris Deugau]

For things like Office365 migrations, where multiple records need to be added, and where those have sometimes been requested on a schedule combined with other changes, a batch command system would speed up entry quite a lot.\

Commands should include things like:

removemx (clears all MX records as of command issue)
importBIND (import BIND-formatted records, possibly just in a block with an Obvious(TM) terminator string?)