Fix repeater issue in transaction list

[reyraa]

Expected behaviour

Multiple pending transaction in transaction list must be possible.

Actual behaviour

Having multiple transaction in transactions list we face this error:
Error: [ngRepeat:dupes] Duplicates in a repeater are not allowed. Use 'track by' expression to specify unique keys. Repeater: transaction in $ctrl.transactions track by transaction.id | orderBy:'-timestamp', Duplicate key....

Steps to reproduce

Send some LSK to an arbitrary address. you'll see the transaction labeled as Pending in the transaction list. now before the it's confirmed and its label is changed from 'Pending' to its actual time, create another transaction to any arbitrary address. open the devtools and see the error.