Add some missing translations

There are some places in our code that made it to be not translated.

This patch fixes some small translation problems and adds some static
strings in templates to translation.

Signed-off-by: Sheogorath <sheogorath@shivering-isles.com>

locales/en.json

@@ -113,5 +113,7 @@
 	"Delete user": "Delete user",
 	"Export user data": "Export user data",
 	"Help us translating on %s": "Help us translating on %s",
-	"Source Code": "Source Code"
+	"Source Code": "Source Code",
+	"Powered by": "Powered by",
+	"Register": "Register"
 }