Bug 9755: Refactor record merge functionality

This patch refactors the merge record interface and code a little bit
in preparation for making it possible to merge authority records.

To test:
1) Apply patch.
2) Try merging two records:
    a) Create a list.
    b) Add two records you would like to (or be willing to) merge
       to said list.
    c) View said list.
    d) Check the checkboxes next to the two records you added.
    e) Click "Merge selected records."
    f) Choose a merge reference.
    g) Choose fields from each record that you want to keep.
    h) Click "Merge."
3) Confirm that your merged record has the fields and subfields you
   wanted.
4) Run the unit tests for the two files that were changed:
    prove t/Koha_Record.t t/db_dependent/Koha_Authority.t
5) Sign off.

Signed-off-by: Mathieu Saby <mathieu.saby@univ-rennes2.fr>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Bug 9755 QA follow-up: move MARC-specific functionality to utility class

This follow-up moves all the MARC-specific functionality of Koha::Record
(now renamed to Koha::MetadataRecord) to a Koha::Util::MARC utility class.

To test, run relevant unit tests:
> prove t/Koha_MetadataRecord.t t/Koha_Util_MARC.t t/db_dependent/Koha_Authority.t
and optionally try to merge a record.

Signed-off-by: Mathieu Saby <mathieu.saby@univ-rennes2.fr>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Bug 9755 QA follow-up: fix template compliance

Fix the following test failure:
* koha-tmpl/intranet-tmpl/prog/en/includes/merge-record.inc                FAIL
    forbidden patterns          OK
    tt_valid                    FAIL
            lines 10, 24
    valid_template              OK

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Passes all tests and QA script.
Found a pre-existing problem with non-repeating subfields
that I noted on the bug report.
All other tests were ok and merging records worked nicely.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Bug 9755: (follow-up) tweak test for tag visibility in merge hash

Koha's MARC framework structure doesn't assign tags to tabs in
the cataloging editor; only subfields are assigned to tabs, and
the field as a whole follows the subfields.

Consequently, for the purpoase of calculating a merge hash, a field
should be added either if no MARC framework information is passed
(which signals that the caller wants to deal with the entire MARC
record) or if any of its subfields are assigned to visible tabs.

This patch has the effect of getting rid of the following spurious
warnings from the Apache log:

merge.pl: Argument "" isn't numeric in numeric ge (>=) at /home/gmc/koha/Koha/Util/MARC.pm line 78

Signed-off-by: Galen Charlton <gmc@esilibrary.com>