Port RPN calculator (alt) face

[redraw]

Here's a PR to port the RPN calculator alt face by @wryun plus some minor features.

Mixing reverse polish notation and a binary-search number input might be confusing for some but I personally love it. Also, the way it switches to scientific notation on big/small numbers, which I think it is not trivial to achieve by input digits individually. Definitely esoteric, but clever considering we have only two buttons.

• Fix secondary index missing POP stack operation
• Add OVER stack operation (a b -- a b a)
• Refactor main loop into mode handler functions
• Add a CALC_PEEK mode by long pressing LIGHT button in operation mode, to see the stack
• Add the stack size at top right inside stack operations only
• Port deprecated display string methods to support custom LCD display