Allow to control transaction fees for Litecoin

[dmi-dmi-dmi]

Recently I've made a few transactions over the LTC network and they took enormous amount of time to appear in the blockchain. It seems that the Unstoppable wallet uses low default fee values.

Please add a way to increase fees when creating a new transaction.

If the wallet already provides a way to do this please give me a hint how to do this. Thanks a lot