Improve epu variable inclusion/exclusion handling.

[gsjaardema]

Currently, in epu you can specify which entity variables to transfer from input to output. This can be done via "ALL", "NONE", or specifying one or more variable names. If the variable names are specified, then you can further limit outputting that name on one or more blocks:

--evar var_name:1:3:5

This would output output the variable names var_name on the element blocks with ids 1, 3, and 5.

--evar var_name

Would only output var_name on all blocks.

--evar ALL

Would output all element variables on all blocks (this is the default)

It would be nice to be able to specify that all element variables (or no variables) are wanted on specific blocks. Something like:

-- evar ALL:1:3:5

Which would cause all element variables to be output on blocks with ids 1, 3, and 5 and no variables on the other block(s).

There is some complications as in:

--evar ALL:1:3:5,mises:2:4:6,eqps:2

All variables on blocks 1, 3, 5; mises on blocks 2, 4, 6; and eqps only on block 2.