REST database module for RemoteCP Panel

Add a database module to the REST framework for general database tasks (groups/sites list)

Other filesystem options for RemoteCP Web

Currently only MySQLfs is available for storage of website files. We should add: NativeFS: Use the normal filesystem for directory structure and data HybridFS: Use MySQLfs for directory structure and normal filesystem for data (using NativeFS)

Cache queries to maximize performance for MySQLfs

There are too much identical queries send by MySQLfs when showing a directory listing in admin.php, just for an empty root directory 11(!) identical queries are send.