Added Unit Variable to ExerciseLog Export

[anuragkanungo]

Fixes #2947

[anuragkanungo]

Atleast for the entries we are sure about unit, let assign them the unit variable and keep others as 0.

If the unit variable is 101-104 then its displaying the correct unit as per our prediction.

But if the unit variable is 0 then we are not sure about the unit, 99% chances are that the unit is the current_unit.

As we can't predict the current unit on the central server, its better to have the value as 0 and let the coaches know that it is most probably the current unit number.

[jamalex]

This should work for the majority of needed cases, so let's get it merged for now, and we can refine later.