Add ability to upload images to backend

[miketaylr]

Screenshots are super helpful for bug reports. We should consider adding this ability to our form and hosting images ourselves (or via a 3rd party API like imgur).

[karlcow]

The chinese version of Firefox has a screenshot feature, because it is one way for people to share images on social network. It's too complicated for many users to save as an image, etc. So they take a screenshot that they can share. It's quite cool.

So looking from where it could come from I checked MDN. I wonder if other browsers have similar APIs.

[miketaylr]

Sorry for all the noise here. Just organizing my thoughts. We have 2 related Milestones:

1. Image uploading
2. Add a screenshot feature

2 depends on 1.

[miketaylr]

There will be 3 possible ways to upload an image:

1. When reporting an image, there should be an input[type=file]
2. When commenting on an image, there should be an input[type=file] (in addition to dragon drop, eventually) 🐉 🐲
3. When reporting an image from one of our addons that supports some sort of a screenshot API

Here's how I see this working for us, roughly:

For issue creation:

1. The file is uploaded and returns a URI pointer to the file
2. That URI is embedded in the issue body using GitHub image markdown syntax: ![file name here](http://path/to/image/)
3. (I think GitHub uploads all these to their own CDN)

For issue commenting:
Same thing, but included inside a comment rather than the issue body.

[miketaylr]

Testing something

[miketaylr]

3. (I think GitHub uploads all these to their own CDN)

So, that's true for true uploads. If you just provide a link to an image, it uses a content proxy:

https://cloudup.com/iSnv2nObVWn