WIP: load an options file everywhere to avoid repetition

Note that I didn't yet remove the "Set Default Proof Using" everywhere, this is just trying the general concept. Thanks to @janno for your help!

This fixes #66 (closed).

build/check-options.sh

+#!/bin/bash
+set -e
+
+for file in $(find -name "*.v"); do
+    if [ "$file" != "./theories/iris_options.v" ]; then
+        if ! fgrep "Load iris_options." "$file" >/dev/null; then
+            echo "iris_options are not being loaded in $file."
+            exit 1
+        fi
+    fi
+done