Improve player_handicap icon implementation

Improve player_handicap icon implementation

Changed the handicap_total calculation method to average given and taken, instead of multiplying them.
Made .handicap_level range from 0 to 16 instead of to 255, so the player_handicap icon will essentially be \xFFF, \xFEE, ..., \xF00 from 1 to 16.
Added HANDICAP_MAX_LEVEL_EQUIVALENT, set to 2, the cl_handicap at which .handicap_level 16 is reached.
Improved some associated comments.
Fixed ".handicap_total" typo.