Allow deletion of transactions

[mweinelt]

This would delete the transaction with the id: 32

But it does not. Make deleting transaction work.

[fleaz]

Make deleting transaction work.

Doesn't your mum told you to say 'please'? ;)

Also I first wanted to implement this feature when OpenSplit/opensplit-backend#13 is finished. Otherwise one could completely fuck up a group and nobody would be able to know what is going on

[mweinelt]

Sugar daddy commands you!