debian/icedove.links: adding /u/b/i link

The CDBS creates the links while building, now just let debhelper doing
the linkage.
debian/icedove.dirs: adding helper file for needed directorys
debian/icedove.install: sort entrys alphabetical
debian/icedove.js: fix small typo and reformating
debian/rules: adding override for dh_fixperms
debian/rules: adding override for dh_install

calendar-google-provider and iceowl-extension needs special handling, we
repack the already created *.xpi files later. So we have to extract them
first.
Because of the branding we also have to install our own icons for the
Icedove grafics.
The icedove-dev package doesn't needs to ship the
lib{mozalloc,mozjs,xul}.so. We link them to the librarys which comes
with the standard icedove package. Removed for depulication.
debian/rules: adding override for dh_shlibdeps
debian/rules: adding override for dh_builddep
debian/rules: correcting Icedove version inside icedove.pc while install
debian/rules: adding override for dh_strip

Without the additional argument for dh_strip the icedove-dbg package
isn't builded.