fix(agama-pw): need to rearrange documentation assets and READMEs

[ossdhaval]

Currently, assets (gif, images, etc) are kept at the top level of the repository. For example, addclient.gif, pw-generated-code.png. All these files are not useful when project gets renders in the Agama Lab, nor Agama Lab can run these files when clicked, like GIF. See the image below:

Suggestion: Move all these files under a directory docs and refer it from there

Plus, there are README files at various levels which will be never used, but since they are there in the GH repo, the READMEs become part of Agama Lab nav bar as well and add to the clutter.

Suggestion: remove the files if they are not needed