Add an axis aligned box in the geometry module.

Some naming questions:
- for "extend" we could also think of: "expand", "union", "add"
- same for "clamp": "crop", "intersect"
- same for "contains": "isInside", "intersect"
=> ah "intersect" is conflicting, so that eliminates this one !

test/CMakeLists.txt

@@ -166,6 +166,7 @@ ei_add_test(svd)
 ei_add_test(geometry)
 ei_add_test(hyperplane)
 ei_add_test(parametrizedline)
+ei_add_test(alignedbox)
 ei_add_test(regression)
 ei_add_test(sparse )