Use gettext .po files for translations

This allows the same workflow as most other projects for translations.

po/Makefile

@@ -0,0 +1,29 @@
+all:
+.PHONY: update-po update-js update-pot
+
+LINGUAS := de el nl sv
+
+VERSION := $(shell grep '"version"' ../package.json | cut -d '"' -f 4)
+
+POFILES := $(addsuffix .po,$(LINGUAS))
+JSFILES := $(addprefix ../app/locale/,$(addsuffix .js,$(LINGUAS)))
+
+update-po: $(POFILES)
+update-js: $(JSFILES)
+
+%.po: noVNC.pot
+	msgmerge --update --lang=$* $@ $<
+../app/locale/%.js: %.po
+	./po2js $< $@
+
+update-pot:
+	xgettext --output=noVNC.pot \
+		--copyright-holder="Various Authors" \
+		--package-name="noVNC" \
+		--package-version="$(VERSION)" \
+		--msgid-bugs-address="novnc@googlegroups.com" \
+		--add-comments=TRANSLATORS: \
+		--sort-by-file \
+		../app/*.js \
+		../core/*.js \
+		../core/input/*.js