Feature/grpc for discovery

[emmlejeail]

sdk with grpc feature for discovery is ready to be merger with master

[CLAassistant]

All committers have signed the CLA.

[johanstokking]

Adding:

• @dotpy3 for checking Python code
• @romeovs for consistency with node-app-sdk

Also, please reword commit messages and follow conventions in new CONTRIBUTING.md, e.g.:

• Do not mention what files are added or changed, we can see that by looking at the changed files. Instead, mention what you changed
• Amend to a commit if you fix or extend something
• Use lowercase and short prefixes, e.g. doc: X instead of Documentation: X

[johanstokking]

I'm with @dotpy3 for review

Seeing the commit trail; should we squash instead of merge?

[emmlejeail]

@johanstokking If you think that's best let's squash everything into master

[johanstokking]

OK yeah the trade-off is better history. The last part is clean, good work there.