medium: term: Handle $ in input when rendering (bnc#893011)

If an attribute contains a $ character at the end, it would be followed by a ${..} highlighting entry if colorized. The term renderer would then detect it as a $$ sequence, throw an exception and spit out the raw ${..} codes to the terminal. Instead of doing this, we now don't try to detect $$ sequences (because we had no sensible handling of them anyway) and instead of letting the ${...} pass through, replace it with an empty string.