AggAllParticipants doesn't need dates

[jgbarah]

Currently, AggAllParticipants in ITS.R is called as:

AggAllParticipants (startdate, enddate)

but it doesn't seem to use (nor needs) dates at all. If I'm right, those two arguments should be removed.

[dicortazar]

Well, at some point that function should calculate all participants between two days. So far this is only calculating that value for the whole project.

[jgbarah]

In that case, I guess it should have at least a comment, stating the reason, but probably default values for each parameter, which could be NA, so that it can be used without parameters when needed (which is now always).