Refactor ipfs-companion so it no longer sets properties on the window

[alanshaw]

This PR refactors the ipfs-companion module so it no longer sets properties on the window object.

I'm viewing the ipfs-companion module as something I'd like to create an instance of, or multiple instances of, and also teardown - with the end goal of making it easier to reason about, maintain and test. So this PR stops it from setting properties on the window object and instead init returns an API object which is the method one should communicate with the module.

background.js, after creating the new instance, sets it to window.ipfsCompanion so that the popup, quick upload and options pages can make use of it's API.

• Pulls out the notifier logic into it's own module
• Pulls out the copying logic into it's own module
• Uses port.postMessage to signal to the companion to perform a copy (instead of calling the functions on the background page)
• Refactors some of the async FileReader logic into async/await style

[lidel]

@alanshaw Looks good, I see how this will make writing tests easier 👍

The only thing blocking merge is a non-invasive error logged on initial load.
It is the same in both Chrome:

and Firefox:

It does not impact functionality, the contextMenuUploadToIpfs menu item is eventually initialized and works fine, but the error should be somehow addressed.

[alanshaw]

@lidel ok all fixed up - I moved the context menu initialisation and update stuff into the context-menus module and that has fixed it.

[olizilla]

This is quickly going to get difficult to merge with #320 and friends, so I'm gonna take a look at it now and see if it's good to go 🚀✨ 👀

[olizilla]

Looks good, test pass, and works for me in Firefox and Chrome. 👍 ✨

[olizilla]

@lidel do you have a minute to merge this? Merging is blocked on re-review. In retesting this I can see the error message has been resolved.

[lidel]

@olizilla my apologies, I run out of time to review this yesterday.

Old error is gone, but now I get this one on every API poll (while external node is down):

ReferenceError: can't access lexical declaration `offlinePeerCount' before initialization  background.js:360:

Are you able to reproduce? If not, it may be the machine I am on, I'll retest on another one in 5h.

[olizilla]

@lidel yes, good spot, I'm seeing that too. @alanshaw can you take a look when you get a moment?

[olizilla]

Actually, I see the problem... pesky hoisting / lexical scoping. Am fix.

[lidel]

Thanks! 👌