Add an option for Electro combos to deal damage over time for better area control

Implements an option to have the Electro's secondary combo deal damage over a duration rather than instantly, reducing the weapon's burst potential and helping it shine where it's supposed to: as an area control weapon.
A new particle effect is included to aid in the visuals of this new behaviour, it will fallback to the existing hook bomb effect if it doesn't exist making this compatible with older clients.

The new behaviour can be activated with test_electro_combo_over_time or the following settings:

g_balance_electro_combo_duration 1.5
g_balance_electro_combo_force 0
g_balance_electro_combo_damage_linear 1