Oncomming release 0.4.1

Tomorrow is date for oncomming release 0.4.1 and comes mainly with fixes against 0.4.0. It brings the following advantages:

• removed tact, meaning BPM is the only segmentation
• fixed drum playback button
• ability to stop sequencers by toggle play
• enhanced notation editor, channel editing is turned on by default

There still some issues won't be fixed but is certainly a great step towards usability.