pingo. Minor code reorg in shader manager.

Remove using std statement.
Move convenience types inside pingo namespace.
pingo. Additional shader manager changes.

Remove the GLES shader manager type.
Minor change to program key is produced in shader manager.
pingo. Changes to shader.

Change GLES shader to not use the gl object as base class.
GLES shader is now derived from shader directly.
Changes to shader initialization, shader creation is now done directly from code.
Shader code is provided by the shader manager.
This is a preparation step to enable placing shader code in assets.
pingo. Implement loading shader from asset files.

Remove the shader code constants from shader manager.
Implement code for loading shaders in shader manager shader access method.
Load the shader from an asset file if it's hasn't been loaded yet.