Bug 14277: add zebra indexes for lexile that respect 521 indicator 1.

Bug 14277: add zebra indexes for lexile that respect 521 indicator 1.

Added the following indexes:

Interest-age-level | 591$a ind1=1
Interest-grade-level | 591$a ind1=2
lexile-number | 591$a ind1=8
Reading-grade-level | 591$a ind1=0

Moved 'lex' from a zebra index to a ccl alias to lexile-number.

Changed the handling of st-numeric in C4/Search.pm to allow for search ranges.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Hector Castro <hector.hecaxmmx@gmail.com>
Works as advertised
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>

Signed-off-by: Jesse Weaver <jweaver@bywatersolutions.com>