Add folder dropping, fix rate limits

- Add folder drag and drop support
- Do expodential retrying if rate limited, allowing upload of very large drive folders
- Do not import deleted files
- Move the upload buttons to their own line
- Notify when no TJA files have been found
- Add more translations

public/src/views/customsongs.html

@@ -1,12 +1,24 @@
 <div class="view-outer">
-	<div class="view">
+	<div class="view drag-bg">
 		<div class="view-title stroke-sub"></div>
 		<div class="view-content"></div>
-		<div class="left-buttons">
+		<div class="center-buttons">
 			<div id="link-localfolder" class="taibtn stroke-sub link-btn"></div>
 			<div id="link-gdrivefolder" class="taibtn stroke-sub link-btn"></div>
 		</div>
 		<div class="view-end-button taibtn stroke-sub selected"></div>
+		<div class="view-outer shadow-outer" id="dropzone">
+			<div class="view">
+				<div class="view-content"></div>
+			</div>
+		</div>
+		<div class="view-outer shadow-outer" id="customsongs-error">
+			<div class="view">
+				<div class="view-title stroke-sub"></div>
+				<div class="view-content"></div>
+				<div class="view-end-button taibtn stroke-sub selected"></div>
+			</div>
+		</div>
 	</div>
 	<form><input id="browse" type="file" webkitdirectory multiple></form>
 </div>