Change to calculator UI

[#247](https://github.com/Gizra/IBLI/issues/247)
![selection_009](https://cloud.githubusercontent.com/assets/7369740/4540229/936f5942-4e05-11e4-896f-79d3c1feb316.png)
![selection_010](https://cloud.githubusercontent.com/assets/7369740/4540232/97d7f02a-4e05-11e4-9722-22ed3954ea23.png)

@niryariv How does this look ?