Refactoring: move all code files into a src directory

src/UI/BigComponents/OpenBackgroundSelectorButton.svelte

@@ -0,0 +1,21 @@
+<script lang="ts">
+  /**
+   * A mapcontrol button which allows the user to select a different background.
+   * Even though the componenet is very small, it gets it's own class as it is often reused
+   */
+  import { Square3Stack3dIcon } from "@babeard/svelte-heroicons/solid"
+  import type { SpecialVisualizationState } from "../SpecialVisualization"
+  import Translations from "../i18n/Translations"
+  import MapControlButton from "../Base/MapControlButton.svelte"
+  import Tr from "../Base/Tr.svelte"
+
+  export let state: SpecialVisualizationState
+  export let hideTooltip = false
+</script>
+
+<MapControlButton on:click={() => state.guistate.backgroundLayerSelectionIsOpened.setData(true)}>
+  <Square3Stack3dIcon class="h-6 w-6" />
+  {#if !hideTooltip}
+    <Tr cls="mx-2" t={Translations.t.general.backgroundSwitch} />
+  {/if}
+</MapControlButton>