BibSort: improved washers

• Improves speed and realiability of BibSort washers by properly exploiting textutils.decode_to_unicode() and textutils.translate_to_ascii() functions. (PR #2283)

• Improves speed of textutils.translate_to_ascii(). (addresses #1754)

• Introduces new washer _sort_nosymbols_case_insensitive_strip_accents().

• Makes unidecode dependency mandatory.

Signed-off-by: Samuele Kaplun <samuele.kaplun@cern.ch>
Tested-by: Tibor Simko <tibor.simko@cern.ch>