adds feature to aggregate identical CombatPreview ModifierStrings

[slothoth]

In the unit Combat Preview, strength modifers are listed, even if the values are identical. This can lead to UI bloat if many modifiers are present, as seen in the modded example.

To fix this, Modifier strings are stored and duplicate strings are instead aggregated, I.E. In the mod example, I have given the Battlecry promo a second copy of its normal modifier, but instead of +7 twice, it sums it as +14.

I am planning on releasing this change with my own associated mod, but other modders have expressed interest in using it, but are not Lua programmers. I figured a good comprise might be a home in CQUI.