Real Time Render Functionality

[wip-abramson]

@jandrieu I have added the ability to turn off real time rendering of markdown.

Need to decide where and how this should work.
Eg.
Should this be visible in production?
Should this just be a feature of edit mode? If so how does someone render? - Save possibly?
What should we name the menu item?
Which menu should it go under?

[jandrieu]

Maybe a checkbox for Render realtime? Only shown on edit.
And, yes, always render on save.

[jandrieu]

I made this MVP because I was getting crashes from the rendering process.

[wip-abramson]

I have added the checkbox for this. @jandrieu you mentioned some shortcut to render without saving, how do you imagine this working?

[wip-abramson]

Move checkbox to file menu. On toggle real time render then render the document