qt: Remove thousands separators after decimal point

Revert thousands separators after decimal point, as introduced in #4167.

I've tried and tried and just cannot get used to these. And if someone like me with a scientific background can't get used to them, I'm sure many other people will have problems with them.

If you don't want to see a long string of decimal digits, switch your unit to mBTC or muBTC.

Before
![with](https://cloud.githubusercontent.com/assets/126646/4182905/d7743c66-3735-11e4-97d0-b2805931423f.png)

After
![without](https://cloud.githubusercontent.com/assets/126646/4182906/dadd08ec-3735-11e4-8191-379e1d5fdf28.png)