espeakedit: version bump 1.46.02 -> 1.48.03 (and add to channel)

The one-liner gcc buildPhase doesn't work anymore, so I'm using upstream
Makefile instead. The Makefile needs a tiny patch to work (not nixpkgs
specific).

Also fixup path to 'sox' and espeak-data/ (runtime deps) by providing
full paths.

TODO:
Uhm, seems like espeakedit still wants espeak-data/ in $HOME, even
thought I've told it to use $espeak/share/espeak-data. Have to contact
upstream to get this fixed.

Workaround: cp -r $(nix-build -A espeak)/share/espeak-data ~