[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"});