casio/pickytlk.cpp: Add tablet support

[qufb]

Most screens can now be interacted as expected. Some additional changes include:

• Add a new flag register bit, which is used for detecting when the pen is pressed and then hold down;
• Remove the last column from the LCD display, which now matches the visible area in hardware;

[qufb]

@cuavas Do you have any concerns with the layout stuff done here?

In the meantime I scanned the touchpad overlay for this system, and would likely be preferable to use that instead of the discrete shapes being drawn here for buttons. Probably can be included in software list like Beena carts, although the program ROM is loaded via ROM_START.

Note that the overlay sits on top of the LCD screen, so all the covered area can also be interacted. There's program code logic to match coordinates with the visually distinct buttons, so it shouldn't be implemented with discrete inputs like other overlay layouts.