MinimapFuncBox.cs: added Spring-AI to "AddAI" button

Other files: Added SpringStore.cs, which cache Spring-AI because getting them from Unitsync repeatedly is super expensive! (UnitSync.cs interface might be guilty for this high cost, but that's for later).

SpringsettingForm.cs: also cached Springsetting list (only saved 270ms, but will never need to run Spring.exe to get the list)

The cache is refreshed for different spring. So tiny freeze should be expected when pressing "show Spring AI" for first time.