Special ship upgrades

[icydee]

Some ship upgrades should be special. e.g. 10% increase in stealth, speed etc. These could be obtained by special events, or by missions, or by purchase from time to time from AI.

Upgrades would be empire wide, could be applied retrospectively to existing ships (via the ship 'refit' option) which would ensure that ships could more easily be collected into fleets.

This would also have the benefit of increasing trade options.