Add ability to draw on images before sending them (for mobile apps)

[hoggatt]

This is a feature I use all the time in other messaging applications that I think many people would find useful to have in Element (for the mobile apps specifically). When taking a picture using the app, it would be nice if at the "send" screen you were able to mark up the image. Here's an example of what I mean (although it wouldn't have to be this complex):

This can come in useful in situations where I want to point something out in the image and it's much easier to draw an arrow vs explaining via text. I use this almost every day and would love to see this feature added to element.