Add tool `msgfmt` with libraries

This tool is needed to convert `*.po` files to `*.mo`.
Additional libraries are copied into `$ARCH/lib` folder.

Signed-off-by: Denis Pynkin <denis.pynkin@collabora.com>

external-binaries.cfg

 gettext-base /usr/bin/gettext
+gettext /usr/bin/msgfmt
+gettext /usr/lib/x86_64-linux-gnu/libgettextlib-0.19.7.so amd64,prefix=lib
+gettext /usr/lib/aarch64-linux-gnu/libgettextlib-0.19.7.so arm64,prefix=lib
+gettext /usr/lib/arm-linux-gnueabihf/libgettextlib-0.19.7.so armhf,prefix=lib
+gettext /usr/lib/x86_64-linux-gnu/libgettextsrc-0.19.7.so amd64,prefix=lib
+gettext /usr/lib/aarch64-linux-gnu/libgettextsrc-0.19.7.so arm64,prefix=lib
+gettext /usr/lib/arm-linux-gnueabihf/libgettextsrc-0.19.7.so armhf,prefix=lib