ImportSongs: Implement Google Drive beta testing

Instances that wish to enable Google Drive support should first enable it to only a small subset of users (100 maximum) to allow the OAuth screen to be verified by Google without hitting the user limit. Minimum level in the config can be set to enable beta testing of this feature and then disabled by setting it to None.

- Add user level assignment screen to the administration panel
- Add privacy policy and links to it in various places
- Add switch accounts link near the Google Drive picker

public/src/js/strings.js

@@ -918,6 +918,13 @@ var translations = {
 			tw: "註冊",
 			ko: "가입하기"
 		},
+		privacy: {
+			ja: "プライバシー",
+			en: "Privacy",
+			cn: "隐私权",
+			tw: "隱私權",
+			ko: "개인정보처리방침"
+		},
 		registerAccount: {
 			ja: "アカウントを登録",
 			en: "Register account",
@@ -1135,6 +1142,13 @@ var translations = {
 			tw: "Google雲端硬碟...",
 			ko: "구글 드라이브..."
 		},
+		gdriveAccount: {
+			ja: "アカウントの切り替え",
+			en: "Switch Accounts",
+			cn: "切换帐户",
+			tw: "切換帳戶",
+			ko: "계정 전환"
+		},
 		dropzone: {
 			ja: "ここにファイルをドロップ",
 			en: "Drop files here",
@@ -1180,6 +1194,9 @@ var translations = {
 		},
 		authError: {
 			en: "Auth error: %s"
+		},
+		cookieError: {
+			en: "This function requires third party cookies."
 		}
 	}
 }