Add script to ease workflow with submodules

Signed-off-by: Tobias Frisch <tfrisch@uni-koblenz.de>

scripts/submodules.sh

+#!/bin/sh
+if [ "$1" = "init" ]; then
+	git submodule init
+    git submodule update
+elif [ "$1" = "reset" ]; then
+    git submodule deinit -f .
+	git submodule update --init
+elif [ "$1" = "update" ]; then
+    git submodule foreach git pull
+fi
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