update translation template and add file context for each string

The file context lets the translators know which command the string applies
to.  It does not have line numbers, since those are less useful, while
causing lots of merge conflicts.

locale/Makefile

@@ -23,7 +23,7 @@ template: $(TEMPLATE)
 $(TEMPLATE): $(FILES)
 	xgettext --join-existing --from-code=UTF-8 \
 		--language=Python --keyword=_ \
-		--sort-output --no-location --output=$(TEMPLATE) \
+		--sort-output --add-location=file --output=$(TEMPLATE) \
 		--package-name="fdroidserver" --package-version=$(VERSION) \
 		--foreign-user \
 		--msgid-bugs-address=https://gitlab.com/fdroid/fdroidserver/issues \