Second footer for Capacity added, shown in equipment market

Issue3117 implementation.
Summary:
- Added two new lines to ship info screen: Cargo space(available for cargo/ship maximum cargo capacity), Cargo space used(same as on the station view).
- Modified TabView to use unique footers for tabs(maybe not the best solution) so on the equipment market screen the capacity gauge is shown instead of the cargo gauge. Drawback: there are two footers now with duplicated ui elements and subscriptions to value changes because a ui element can be attached to one container only. 

Leftover/to discuss:
- I needed to add a new text entry: CARGO_SPACE_USED, it is only added to en.json atm.
Any idea to avoid adding this new entry? or just dump this line?
I tried with another language and there is no fallback to English(so the game crashed) why is that? Ugly text is better than nothing imo :)