Allow Macros to contain one variable selector

[Zrp200]

Currently, macros only allow selectors as the last command, which is pretty useless.

The limitations of selectors in SPD only prevent initializing another selector after a first one.

Implementation should consistent of passing control back to the executing macro after a cell is selected, so a macro consisting of

@terrain use terrain %1
@cell cell
use level set @cell @terrain
use gamescene updatemap @cell 

would correctly prompt for a cell to be selected and then set that cell to the passed terrain.

Bonus points if the variable can be restricted to only exist inside of the variable.

[Zrp200]

Should probably also give a way to pass a cell directly to existing scroll of debug commands that currently take selectors, as that would allow those to be tied into macros.