Bugfix in render view to make frustrum (kinda) work with overwritten projection.

We need this to make the AR examples work.
Started implemented asynchronous Xflow operators. Everything untested.
Added basic (kinda hacked) support for asynchronous Xflow operators.
Implemented proper checks for asynchronous operator execution.
Added noAlloc option for Xflow operator output.

If noAlloc is enabled, no output buffer is allocated and passed to the operator.
Instead, a object with the member "assign" is passed.
The operator can allocate its own buffer/image and assign it via
[output argument].assign = [buffer / image];

See the xflow.bufferSelect operator for an example.
Change for async executer: do not set connected processing nodes as processed.
Added new CHANGED_SIZE_TYPE notifier in Xflow to avoid potential problems.

CHANGE_SIZE_TYPE will be fired when a parameters changes between the states "null", "single" (uniform) and "many" (vertex).
It will trigger a STRUCTURE_CHANGED event for results.
Merge branch 'xflow-async' into develop
Added more filter types
Made linear-mipmap-linear the default value for filterMin
Refactor texture handling in XFlow and XML3D.

Floating point textures are now supported using Float32Array and extension.
Canvas, Image and Video handling unified through TexelSource class.
Further testing and refactoring necessary.

Signed-off-by: Jan Sutter <jan.sutter@dfki.de>
Add different formats and types to Xflow textures

Signed-off-by: Jan Sutter <jan.sutter@dfki.de>
Add RGBE PNG to float texture operator

Signed-off-by: Jan Sutter <jan.sutter@dfki.de>
Fix bug in NPOT image scaling

Signed-off-by: Jan Sutter <jan.sutter@dfki.de>
Minor changes in TextureEntry

Signed-off-by: Jan Sutter <jan.sutter@dfki.de>
Fix mipmap NPOT scaling bug

Signed-off-by: Jan Sutter <jan.sutter@dfki.de>