Text areas

[nsreed]

Add support for text areas, at a minimum, this should include:

• Adding a text box with predefined text
• Editing existing text boxes

[ultimape]

There is no way to set a default size despite a size slider being present when editing.

See also #53 with an issue about not being able to change size.

[nsreed]

Clarified that "size" is actually "stroke width", as well as adding an explicit field for "font size"