Add additional RPC calls

[ghutchis]

Right now, there are two main JSON-RPC calls:

• openFile(filename)
• loadFile(data)

There's a definite need for other JSON-RPC calls to help with automation / scripting:

• saveFile(format) => bytestream or string
• saveFile(format, filename) => force a save
• renderImage(filename) => render current frame buffer
• renderAnimation(options) => step through coordinates to render the whole reaction / trajectory, etc.

I can imagine requesting particular rendering options would be useful

Some level of security analysis is needed (e.g., to make sure malformed request don't crash Avogadro, and to ensure RPC can be turned off as a preference even if compiled in).

[ghutchis]

I'd also love to see a way inside a Jupyter notebook:

• launch Avogadro
• go back to the notebook and request the current molecule to be saved / passed to the notebook
  • (for example this might use the saveFile() RPC call above)

This probably requires an "rpc" component as part of the Avogadro / OpenChemistry Python module.

[ghutchis]

Not that this needs to be a project for @cryos - but ideas or other RPC methods would be welcome.