Move shares (#1812)

From ./data/ to ./app/
Fix manual updates like
https://github.com/FreshRSS/FreshRSS/issues/1803#issuecomment-369371907
Left for later: support a ./data/shares.local.php for user-defined
shares.

app/FreshRSS.php

@@ -128,7 +128,7 @@ class FreshRSS extends Minz_FrontController {
 		}
 		header("X-Content-Type-Options: nosniff");
 
-		FreshRSS_Share::load(join_path(DATA_PATH, 'shares.php'));
+		FreshRSS_Share::load(join_path(APP_PATH, 'shares.php'));
 		self::loadStylesAndScripts();
 	}
 }