New feature: Calculations inside Events detail bracket

Calculation features:

Now you can make some simple (+, -, *, /) calculations inside the brackets with the following Parameters:

Invited guests; Accepted guests; Guests limit; Seats available.

For example:

If ${"Invited guests"} generates 5

and ${"Accepted guests"} generates 1

then ${"Invited guests - 2"} will generates 3

and ${"Invited guests - Accepted guests"} will generates 4