Moved CreateFilter to RenderScript

Also promoted m_Filter to protected, otherwise it's extemely hard to
overrule RenderScript's behaviour.

At any rate, ConfigurableRenderScript should behave identical to
earlier, so only RenderScriptChain required modification.

That said, for some reason Resizer didn't allocate texture anymore,
which is odd since I couldn't find out why it even allocated them in the
first place. Fixed by changing TextureAllocTrigger.

Also Intialize filters automatically using HandleFilterChanged. And made
RenderScript dispose m_Filter, this turns out to be more convenient if GetFilter
isn't overriden.