[iOS] Add support for change default database path.

Possible values:

docs: Documents (Default, if no set)
lib: Library
caches: Caches
tmp: Temporary
Example:
var db = window.sqlitePlugin.openDatabase({name: "myDB", path: "docs"});
var db = window.sqlitePlugin.openDatabase({name: "myDB", path: "lib"});
var db = window.sqlitePlugin.openDatabase({name: "myDB", path: "caches"});
var db = window.sqlitePlugin.openDatabase({name: "myDB", path: "tmp"});