Add dialog showing diff of changes to save

Add a save dialog at the bottom of the screen that is present whenever
there are unsaved changes.  This dialog provides a diff between the
client and server state so that the user can easily confirm the changes
they are about to make are the correct changes before applying them to
the server.

components/DiffSchedule.vue

@@ -0,0 +1,64 @@
+<template>
+	<div>
+		<h2>Changes</h2>
+		<section v-if="locations.length">
+			<h3>Locations</h3>
+			<DiffScheduleLocation
+				v-for="location in locations"
+				:key="location.id"
+				:location
+			/>
+		</section>
+		<section v-if="events.length">
+			<h3>Events</h3>
+			<DiffScheduleEvent
+				v-for="event in events"
+				:key="event.id"
+				:event
+				:schedule
+			/>
+		</section>
+		<section v-if="roles.length">
+			<h3>Roles</h3>
+			<DiffScheduleRole
+				v-for="role in roles"
+				:key="role.id"
+				:role
+			/>
+		</section>
+		<section v-if="shifts.length">
+			<h3>Shifts</h3>
+			<DiffScheduleShift
+				v-for="shift in shifts"
+				:key="shift.id"
+				:shift
+				:schedule
+			/>
+		</section>
+	</div>
+</template>
+
+<script lang="ts" setup>
+const props = defineProps<{
+	schedule: ClientSchedule
+}>();
+
+const locations = computed(() => {
+	return [...props.schedule.locations.values()].filter(location => location.isModified());
+});
+const events = computed(() => {
+	return [...props.schedule.events.values()].filter(event => event.isModified());
+});
+const roles = computed(() => {
+	return [...props.schedule.roles.values()].filter(role => role.isModified());
+});
+const shifts = computed(() => {
+	return [...props.schedule.shifts.values()].filter(shift => shift.isModified());
+});
+</script>
+
+<style>
+h2 {
+	margin-block-start: 0.2rem;
+}
+</style>