[FIX] remote.getPendingTransactions sets _clientID now correctly

getPendingTransactions in remote sets transaction.clientID instead of transaction._clientID. 
Because of this calls to saveTransaction are made with empty clientID, and the database entry never got updated. 

I also added a remote testcase which ensures _clientID is set.

I'm not sure why clientID was changed to _clientID, but looking where these changes were made i guess this fix uses the intended behavior.

Passes all tests in develop branch locally.