[FEATURE] Add UI support for Internationalized Domain Names (IDN)

Add support for inputting and converting IDN domains in TCEforms.

The domain is still stored and processed as punycode, only the user is
now able to also enter also the IDN with its special chars in the
backend.

Include 3rd-party converter class "IDNA Convert"

Change-Id: I87d275a2f3bcfd321147b6d32a5403db704bdc4d
Resolves: #14500
Releases: 4.6
Reviewed-on: http://review.typo3.org/3804
Reviewed-by: Steffen Gebert
Tested-by: Steffen Gebert