Also some PKGBUILD rework

All the autotools builds are ported to meson now.

nemo-preview ported to meson, so adapt build pattern to suit

Forgot to remove this even though it's no longer checked for in the configure
script as of this release.

Plus fix for python3.8 support... yet another fallout of python3-embed. I PR'ed
this but not until after the tag was cut...

samurai is <3

nemo-python ported to meson
add optdepends on cinnamon-translations where appropriate

Do lots of cleanup. Drop useless deps, fix nemo-seahorse missing its files
which cannot use nautilus, dramatically simplify build process.

Drop no-longer-necessary python2 fix.

FTR, commands used to change arch=() and then verify the changes:

$ sed -Ei "/^arch=/{s/ *?['\"]?i686['\"]? *?//;s/ *$//}" */*/PKGBUILD*

$ grep -r i686 * | grep arch= | grep -v repos

$ svn diff | grep -A 1 ^-[^-] | grep -v -- -- | cut -c2- |
  while IFS=$'\n' read -r l1; IFS=$'\n' read -r l2; do
    echo "$l1 -> $l2"
  done | sort -u