Bug 16371: Combine get_daily_quote and get_daily_quote_for_interface

Bug 16371: Combine get_daily_quote and get_daily_quote_for_interface

This patch combines get_daily_quote and get_daily_quote_for_interface
methods and moves them from Koha::Quote to Koha::Quotes. Also removes
some unused code and adjusts datetime parsing.

To test apply this patch and confirm 'QuoteOfTheDay' syspref still
works as expected (quote is shown in correct mainpage(s)).

Also prove t/db_dependent/Koha/Quotes.t

Sponsored-by: Koha-Suomi Oy

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>