Fix play time column if no playtime, hide game column if single game

[DasSkelett]

Problem

#3543 introduced play time tracking and tries to conditionally display it in the "Manage game instances" dialog only if any instance has a playtime > 0.

This is broken, because the 0,0 string for the playtime is added to the ListViewItem contents array all the time, and if the column is removed it shows under Path:

Changes

Now the string array for the column contents is factored out into a separate function. It includes the play time string only if the column (header) will actually be present in the end.
The same is applied to the "Game" column now as well, for those that only have instances of a single type of game registered with CKAN (currently the case all the time for everyone as we don't support another game yet).
The auto-resizing needs to be done after removing columns as it applies it to the incorrect columns otherwise.

(Ignore the Factorio instance being present, it is detected as KSP as this current branch doesn't have Factorio support)

I've also added the German localization for the play time strings.

[HebaruSan]

Looks good, let's do this.