iMouse iChannel0 support

[vitos1k]

Hi! I've managed to add support for image textures through iChannel0-10

teximage = bpy.data.images["iChannel0"]
self.texture = gpu.texture.from_image(teximage)

self.shader.uniform_sampler('iChannel0', self.texture)

And it works, shaders are displayed properly, but there is a problem. Shader keeps calling self.cancel and stops refreshing. And i can't find an instance of it, to call Running_modal other than recreating through operator (glsltexture).
Maybe we could add some interface to add custom textures to iChannel channels, and have explicit buttons to call execute and stop refreshing. Maybe i could look into it, but are you available for merging pull requests or should i just fork it and update on my own repo?