[kutil] Add sorted insert to kutil::vector

Added a sorted insert to vector, as well as cleaning up and extending
the removal functions.

src/tests/container_helpers.h

@@ -0,0 +1,13 @@
+#pragma once
+
+struct unsortableT {
+	int value;
+};
+
+struct sortableT {
+	int value;
+	int compare(const sortableT *other) const {
+		return value - other->value;
+	}
+};
+