Improves tab completion in chat.

Pressing tab after completion now cycles to the next candidate.
Merge pull request #6347 from mizipzor/tab-completion

Improves tab completion in chat.
Adds InaccuracyModifier.
Improve accuracy on level-up.
Moved SellSounds from Building to Sellable & added upgrade to rules.
Merge pull request #6344 from reaperrr/accuracy-modifier

Added InaccuracyModifier
Merge pull request #6362 from atlimit8/SellingSounds

Moved SellSounds from Building to Sellable & added upgrade to rules
Complete ArmorModifier->DamageModifier rename

PR #6303 neglected to rename the "armor" upgrade to "damage" in all
necessary places, as mentioned in
https://github.com/OpenRA/OpenRA/pull/6303#issuecomment-53312209