Fix issue with screenshot size

[scottwittenburg]

Currently just fixes the captured screenshot size at 512x512, but could be extended in the future to allow the user to specify an arbitrary size. Depends on this PR getting merged into vtk.js, then we can bump the version we depend on here.

Fixes #99

[jimklo]

@scottwittenburg I've pulled and tried this on our integration environment. I've tried resizing my browser and taking various screen shots, and it's still sending images larger than 512x512 px.

[scottwittenburg]

@jimklo That's because it depends on a change in vtk.js which isn't merged yet. As I mentioned in the description, we need that to get merged and generate a new version, then we can bump our dependency on vtk.js to pick it up. I changed this to a draft.

[aashish24]

@dchiquito could you look over at this issue with help from @scottwittenburg and @dzenanz

[jimklo]

The screen shot issue is somewhat fixed. 512x512 max proportions seems fine. The problem we seem is that there is too much black, and the actual MRI image is very small and low resolution in comparison to the image size embedded in the email.

The browser size and host resolution seems to also still play a variable, as when I took snapshots using my iPad, the scan better fills the 512x512 box, however the image resolution seems low the size.