Change attribute value based on modifier

Returns correct value now

Fixed handling of topups when there is no overusage
Support for a prepaid system

Use summary topup with left over bandwidth from previous month and topups valid for current month to add to cap
Fetches only topups within valid dates now

Added timestamp column to topups

Added date validation feature for checking if the account is allowed to connect or not on the current date

Better error handling

Added Add Many tab for later use