Implement images

[mjakeman]

The next step in reaching the text engine MVP (version 0.2) is allowing for images to be inlined within the view and interacted with using the caret.

The user should be able to:

• Inline images within a paragraph, such that it changes the line height
• Insert images as a block element (i.e. between two paragraphs)
• Select, delete, and modify images using the caret
  • The image should be treated as a one-character-wide object within the model
• Set image size to either be fixed or to fill available space
• Float images to the left or right based on a given anchor point
• Give images alt-text for accessibility purposes (and more generally, implement a11y across the engine)

Not all of this will be available in 0.2 but should be done pre-1.0

• [X] Inline non-text elements
• [X] Line breaking
• [ ] Loading and rendering bitmaps
• [ ] Floats
• [ ] Alt-text