[scrapers] Support XSLT transforms (XML->XML) in the scrapers
cosmetic: indenting
[sorting] don't apply airdate when sorting by year if an empty airdate is specified. fixes #14276
- don't build xsltproc - it pulls in a lot of dependencies which are not available for rbpi (and so linker would try to link in x86 libs found in the system - which fails for arm linkage)
- force our libxml2 - fixes compilation on rbpi
Merge pull request #3758 from jmarshallnz/xslt_scraper

XSLT support in scrapers
Merge pull request #3889 from jmarshallnz/fix_sortlabel_year

[sorting] don't apply airdate when sorting by year if airdate is empty.
[WIN32] changed: used repackaged libxslt and libxml2. No need for the packaging scripts (thanks karlson2k)