* frontend: Added support for message context to localisations.
* frontend: Added string_view versions of the message lookup functions.
* frontend: Added a few more folder options to the internal UI.
* emu/softlist.cpp: Use more appropriate containers.
* Switched to Python 3 by default - this will become a requirement.
* Updated msgfmt.py for message context support.
* frontend: Show all software item info in the internal UI.
* frontend: Search alternate titles in software selection menu.
* 3rdparty/utf8proc: Updated to v2.6.1 (has several fixes).
* frontend: Added software filters for common info fields.
* frontend: Allow UI manager to hold onto persistent session data.
* frontend: Cache software lists for eight machines.
* frontend: Added support for loading localised system names.
* frontend: Add UI for selecting localised system names.
Get rid of a couple of copies of the CC0 text. Add header comment to
CC0 files to remind people editing them what the terms are. Also add
some missing XML headers. The header comments in layouts won't bloat
the binary - they get stripped out before compressing, same as any other
comments.
