IMPORTANT - refactor MARC character set handling

IMPORTANT - refactor MARC character set handling

* IsStringUTF8ish - determine if scalar contains a string in UTF8
* MarcToUTF8Record - convert MARC blob or MARC::Record to UTF8
* SetMarcUnicodeFlag - set appropriate MARC21 or UNIMARC field to
  indicate that record is in UTF-8.

Design points of this module include:

* No dependencies on other C4 modules, making it easier to add
  more test cases
* All character conversion code in one place
* Single entry point for doing a character conversion on a
  MARC record
* Capture of errors and warnings produced by Text::Iconv
  and MARC::Charset
* Start of support for guessing the source character set of
  a MARC record.

Several functions were moved from other scripts
or modules to C4::Charset:

* C4::Koha->FixEncoding (expanded and renamed
  MarcToUTF8Record)
* C4::Koha->char_decode5426
* fMARC8ToUTF8 from bulkmarcimport.pl (renamed
  _marc_marc8_to_utf8)

Several batch jobs were adjusted to use MarcToUTF8Record instead of
FixEncoding.

Signed-off-by: Chris Cormack <crc@liblime.com>
Signed-off-by: Joshua Ferraro <jmf@liblime.com>