Structure tree - show garrisson limit

[elexis]

Many buildings and units (ships, siege) can garrison units. Some of them (iberian) have civ-specific changes. So it would be nice to add this information to the tooltip. As the tooltip is reused in the construction panel, it will appear there too.

To waste less space, an icon could be used insted of text.

[elexis]

In 18455:

Garrison tooltips by fatherbushido.

Show how many units can be garrisoned, the number of arrows shot by default, per unit and limit, fixes #3816.
Thus remove a lot of hardcoded numbers in the translated strings and
correct a wrong number for the mauryan ship, fixes #3904.

[elexis]

Those tooltips are great, the player won't have to compute equations anymore to figure out the projectile limit!

[elexis]

In 18817:

Fix missing maxArrowCount in the GUIInterface causing a wrong projectile tooltip in the session. Reviewed by fatherbushido, refs #3816.

Also unify the garrison limit property names in GUIInterface and Template parsing (thereby also distinguishing a garrison limit of 0 and undefined in that equation).