Add quality tiers to equipment with improved stats.

Quality tiers would not be the same as improved Mk2 and Mk3 variants. These would be in addition to the variants. Higher quality tiers of equipment would be manufactured and possibly be available for an increased cost.

Tier 1: purchased from stations
Tier 2: purchased from stations at an increased cost (1000x?) or manufactured at regular stations
Tier 3: only manufactured at conquerable stations

My recommendations for acquisition are as follows.

Mk1 – One tier.
Mk2 – Two tiers.
Mk3 – Three tiers.

Example stats, not real values:
---------------------------- Dmg --- Vel --- Dly
Plasma Cannon Mk3 -- 750.0 -- 175.5 -- 2.9
T2------------------------- 768.8 -- 179.9 -- 2.3
T3------------------------- 787.5 -- 184.3 -- 2.1