LP#1864516: case-insensitive browse entry display value comparison

LP#1864516: case-insensitive browse entry display value comparison

Following up on bug 1350831, there remains one complaint relating to
"bad data makes browse suboptimal" that can't actually be handled today
by the existing Evergreen code or a pullrequested branch: case differences,
particularly in titles.

We should allow an Evergreen admin to decide on a field-by-field basis
whether case should be considered when determining the uniqueness of a
browse entry coming from a bibliographic record, effectively allowing case
folding. Note that authority fields, being by definition the authorized
value that should be used, do not support this case folding. However, if
authority records are processed first, then bibliographic fields can fold
/into/ those authority fields, achieving the desired result and, in fact,
using the best possible case-preserving display value.

Signed-off-by: Mike Rylander <mrylander@gmail.com>