ImportSongs: Add Google Drive support

- Adds a new page for importing custom songs, where it is possible to pick a local folder (desktop only) or a Google Drive folder (desktop and Android)
  - This feature is disabled on iOS due to the lack of OGG audio support in the browser
- In order to not get rate limited, a TJA file is parsed for metadata only when the song is clicked in the song selection, rather than all at once at import time
- The instance maintainer will need to provide the API credentials in the config.py file to enable this feature
  - This requires a new project to be created at console.cloud.google.com
  - Drive API will have to be enabled
  - API and OAuth keys should be created
    - API key can be restricted to only have Google Drive and Google Picker APIs
    - OAuth Client ID should have Web Application type and JavaScript origins set
    - Editing the OAuth consent screen to have a name and icon is recommended
      - It is semi-required to submit the consent screen for verification as the permission to download all of the Drive files will be asked.
      - Note that the email of the maintainer is publicly visible on the consent screen
  - The project number can be found in the IAM & Admin settings page

public/src/js/strings.js

@@ -102,20 +102,6 @@ var translations = {
 		tw: "遊戲設定",
 		ko: "게임 설정"
 	},
-	browse: {
-		ja: "参照する…",
-		en: "Browse…",
-		cn: "浏览…",
-		tw: "開啟檔案…",
-		ko: "찾아보기…"
-	},
-	defaultSongList: {
-		ja: "デフォルト曲リスト",
-		en: "Default Song List",
-		cn: "默认歌曲列表",
-		tw: "默認歌曲列表",
-		ko: "기본 노래 목록"
-	},
 	songOptions: {
 		ja: "演奏オプション",
 		en: "Song Options",
@@ -1071,6 +1057,43 @@ var translations = {
 		cn: "带歌词",
 		tw: "帶歌詞",
 		ko: "가사가있는"
+	},
+	customSongs: {
+		title: {
+			en: "Custom Song List",
+		},
+		default: {
+			ja: "デフォルト曲リスト",
+			en: "Default Song List",
+			cn: "默认歌曲列表",
+			tw: "默認歌曲列表",
+			ko: "기본 노래 목록"
+		},
+		description: {
+			en: [
+				"Pick a folder with Taiko chart files in TJA format to play on a custom song list!"
+			]
+		},
+		localFolder: {
+			en: "Local Folder..."
+		},
+		gdriveFolder: {
+			en: "Google Drive..."
+		}
+	},
+	gpicker: {
+		myDrive: {
+			en: "My Drive"
+		},
+		starred: {
+			en: "Starred"
+		},
+		sharedWithMe: {
+			en: "Shared with me"
+		},
+		authError: {
+			en: "Auth error: %s"
+		}
 	}
 }
 var allStrings = {}