pobtoken burn_coins with insufficient funds

[buhtignew]

I've noticed that while the pobtoken claim command has the long error message hidden behind the Error: Insufficient funds. output, the pobtoken burn_coins still outputs the version that is not that user friendly.
Maybe we can implement the same short message in this case as well.

[d5000]

This was already fixed in an earlier commit, just tried it and the short red error appears. Closing thus.