The TB2 is a Indiegogo funded 3d printer. It uses a MKS SMELZI V1.0
main board (based on MELZI, i.e. Sanguinololu). I comes as a complete kit,
including display and panel.
Two variants exists, L10 and L16, with a height of 100 and 160 mm.
The heating function of the provided bed can enabled by soldering a
thermistor and some wires to it.

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>

The OLED is driven by an SSD1306, connected to the board via
I2C, the rotary encoder is connected to 3 GPIO pins.

Signed-off-by: Stefan Brüns <stefan.bruens@rwth-aachen.de>

- Make all `unified_bed_leveling` data/methods static
- Move some UBL-related variables into the class
- Replace `map_[xy]_index_to_bed_location` with `mesh_index_to_[xy]pos`

Incorrect optimizations of data types and ternary operators caused some
issues.

UBL's maps are cleaner.   And with a 1 value, G29 O 1  will generate a
map suitable to be Cut & Pasted into Excel so a Suface Map can be
generated.