[box] Option to update all element volume variables when deflecting solution

Allows for volume variables in the box scheme to depend on all dofs of the element.

Adds a 2p3c test with surfactant injection in porous medium (2p3c). The surfactant model is loosely based on the one described here. (Also see here for a longer version). This test will not work without the fix in this MR.

Fixes #892 (closed)