Support ESP+u8g2 with optional bitswap

[plewka]

Somewhere (near SPI Interface?) there is a MSB/LSB swap when using the converter with ESP32 and the U8g2 library which distorts the output. I checked with 1bit per pixel output but added an optional bitswap checkbox, a function to do optional swap and added it to all output functions. The lvgl online converter causes the same problem for my hardware. Maybe there is is something wrong with the u8g but since endian stuff is a traditional and generic issue it's probably a nice feature inside the converter which at least works fine for me.