Two thumb mode in portrait mode

[guancio]

Describe the solution you'd like
Develop a mechanism for using two thumbs.

This is connected to #348 , however I would like to discuss possibilities of using two thumbs specifically in portrait mode. This paper shows the improved wpm when two thumbs are used.
In this settings, splitting/opening the circle is probably unfeasible. However, the left thumb can still be used to click to speed up some operations. For example:

• Click/swipe to accept the letter, so that the thumb does not have to go back to the center circle
• Click/swipe to enter most common letters (e.g. vowels)
• Click/swipe for shift, accents