Added ce_hitevents_healing_crossbow_only

[dalegaard]

When broadcasting, showing all healing events in combattext doesn't look
particularly good. ce_hitevents_healing_crossbow_only stops the combat
text from showing player_healed events, but instead shows all
crossbow_heal events as if they were player_healed events.

Because we are hooking the FireGameEvent method on the
CDamageAccountPanel, we wouldn't normally receive crossbow_heal
events. We utilize our hook on CDamageAccountPanel::ShouldDraw to
catch the first invocation on a given CDamageAccountPanel instance and
subscribe to the event here.

We then add relevant checks and paths in our FireGameEvent hook. When
we encounter a crossbow_heal event, and crossbow-only mode is set, we
create a new player_healed event with matching data and send this to
the original CDamageAccountPanel::FireGameEvent method.