Dot position display

[norberttak]

This PR adds the dot (period) option to display lines.

To add a dot for a given display line, you need to use the dot_position property. The 0 index is the most right dot character.

For example to display 123.45 you have to set the dot_position like this:

[multi_display:id="RADIO_DISPLAY_ACTIVE_UP"]
line="on_select:SW_UP_COM1,dataref:sim/cockpit2/radios/actuators/com1_frequency_hz, dot_position: 2"

closes #105