JS SDK support for devices

[kschiffer]

Summary:
To provide console support for devices (#25), we first need to add support to the JS SDK. Due to the device structure being quite complex, it makes sense to discuss this matter explicitly.

Why do we need this?

• To be able to provide devices CRUD support in the console
• To support devices in the JS SDK (JavaScript SDK #30)

What is already there? What do you see now?

• SDK groundwork and support for applications CRUD
• The CLI's strategy to CRUD devices

What is missing? What do you want to see?

• A (sustainable) strategy for mapping paths to their respective component (NS, IS, JS, AS)

How do you propose to implement this?
Since I see no viable way to get this information automatically, my impulse would be to write a JSON definition that maps the devices fields to the respective component. It would look like this:

{
  "name": "is",
  "description": "is",
  …
  "min_frequency": "as",
  …
  "root_keys": "js"
}

The SDK would then use this definition to decide which component to ask for which path.
Pros:

• Simple and declarative
• Easy to implement

Cons:

• We would need to keep this up to date (by generating this automatically from the protos)

At some later point, when we also generate API code for the SDK, we should also look into providing an automated solution to this issue as well.

What can you do yourself and what do you need help with?
If there is no objection to the strategy explained above, I will start implementing this.

cc @bafonins @htdvisser @johanstokking