Updated installs for basic, default, and shell scripts

Improves name consistency by using the same `install_` prefix for all
install scripts.

The dotfiles script was renamed as a shell script since this is now a
dedicated shell configuration script so people can configure their
default shell as they like. Use of this new shell script will be
configured in a future commit.

bin/install_basics

@@ -0,0 +1,16 @@
+#! /usr/bin/env bash
+
+# Installs basic system settings.
+
+set -o nounset
+set -o errexit
+set -o pipefail
+IFS=$'\n\t'
+
+SCRIPT_PATH="$MAC_OS_CONFIG_PATH/bin/install_basics"
+
+if [[ -x "$SCRIPT_PATH" ]]; then
+  "$SCRIPT_PATH"
+else
+  printf "WARNING: Basic settings script does not exist or is not executable.\n"
+fi