Improved Thermal assistant appearance (enhancement #2368, #2954)

Enchances visibility of thermal assistance information to be able to see it in
shaking glider with a corner of an eye in gauge mode.
Following improvements done:
- Thickened thermal polygon border line
- Thickened and darkened 0 lift line for clearer reference where is lift/sink
- Changed thin dashed outter circle to display MC setting if it is below max lift
and added text value to it
- Changed max_lift text to display actual max value instead of rounded up range
- Thickened and lengthened thermal advisor line with bigger ball at the end
to indicate in which direction the center of the thermal is.