Modified font size setting in text_mode_pypixelcolor

[BAERnado]

I found font_size did not apply if using mode:text however the app does provide this.
I have modified the naming and normalized inputs when sending text as text (not textImage):

1. If font_size is below 16 use 16.
2. If font_size is bigger than device_height use device_height.
3. Only use multiplies of 16. char_height = math.floor(font_size/16)*16