Created dps calculation branch
Damage conversions overhaul.
Added DamageNature class for damage properties matching.
Fixed base damage modifier.
Added support for elemental damage done by weapons.
Renamed Statistics tab in character sheet to Defence.
Added Offence tab to character sheet for offensive attack skill statistics.
Moved all defensive statistic calculations to Compute class.
Added AttributeSet class for working with attributes.
Added calculation of damage ranges for attack skills (except totems, traps, mines and skill cast by support gems).