libreoffice: improvements.

Icons no longer missing (fix #5509).

In `*.desktop` files:

 -  Replaced absolute path to the the store by the program name.

    This is so that files can be dragged elsewhere by the user
    (e.g.: desktop, bar) and still work after upgrade + garbage
    collection and can be shared between machines.

 -  Replace program name `soffice` by program name `libreoffice`
    so that we're sure the desktop file really refers to our
    package's binary and not start office or open office.

Add the possibility of building without the help. This build is
not modular and take a really long time to complete so I want
a mean of improving shortcuts without having to rebuild the
whole thing (see #899). A wrapper script is the next step.

Tested (build and ran the program) with `en_US` only and
without the help module.

pkgs/applications/office/libreoffice/default.nix

@@ -18,6 +18,7 @@
 , libatomic_ops, graphite2, harfbuzz, libodfgen
 , librevenge, libe-book, libmwaw, glm, glew, gst_all_1
 , langs ? [ "en-US" "en-GB" "ca" "ru" "eo" "fr" "nl" "de" "sl" ]
+, withHelp ? true
 }:
 
 let
@@ -136,6 +137,8 @@ stdenv.mkDerivation rec {
     configureFlagsArray=(
       "--with-parallelism=$NIX_BUILD_CORES"
       "--with-lang=${langsSpaces}"
+      "${if withHelp then "" else "--without-help"}"
+      
     );
 
     chmod a+x ./bin/unpack-sources
@@ -176,13 +179,13 @@ stdenv.mkDerivation rec {
 
     ln -s $out/lib/libreoffice/share/xdg $out/share/applications
     for f in $out/share/applications/*.desktop; do
-      substituteInPlace "$f" --replace "Exec=libreofficedev${major}.${minor}" "Exec=$out/bin/soffice"
-      substituteInPlace "$f" --replace "Exec=libreoffice${major}.${minor}" "Exec=$out/bin/soffice"
-      substituteInPlace "$f" --replace "Exec=libreoffice" "Exec=$out/bin/soffice"
+      substituteInPlace "$f" --replace "Exec=libreofficedev${major}.${minor}" "Exec=libreoffice"
+      substituteInPlace "$f" --replace "Exec=libreoffice${major}.${minor}" "Exec=libreoffice"
+      substituteInPlace "$f" --replace "Exec=libreoffice" "Exec=libreoffice"
     done
 
     mkdir -p "$out/share/desktop"
-    cp -r sysui/desktop/icons  "$out/share/desktop"
+    cp -r sysui/desktop/icons  "$out/share"
     sed -re 's@Icon=libreofficedev[0-9.]*-?@Icon=@' -i "$out/share/applications/"*.desktop
   '';