Bug 23159: Reindent addbiblio.tt

Bug 23159: Reindent addbiblio.tt

This patch corrects whitespace in the basic MARC editor template,
addbiblio.tt: Tabs converted to spaces, indentation corrected. Some
comments have been added in the markup to clarify the page structure.

To test, apply the patch and open the basic MARC editor. Confirm that
everything works correctly, including:

 - Showing/hiding subfields
 - Re-ordering subfields
 - Removing tags and subfields
 - Cloning tags and subfields
 - Plugin links

Use the "-w" flag when using diff to examine the patch. The only changes
should be places where single lines were broken up and where comments
were added.

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
(cherry picked from commit c7147fcde03f7ba1ac13e485adcac587f2dde85c)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>