LPS-34905 resizable portal script textarea with memory

Hi Julio,

as promised in https://github.com/juliocamarero/liferay-portal/pull/1733#issuecomment-18175777, here's the revised code, tested with Alloy 2.0. 

The resize handles are not visible due to https://issues.liferay.com/browse/LPS-35460, but it does not influence correct function of this code. Also, there's not a dependency on https://issues.liferay.com/browse/LPS-34903 (sent as https://github.com/juliocamarero/liferay-portal/pull/1812) any more, those two pulls can be used independently.

Thanks,
Josef