Version check on Linux and Windows

[JohnySeven]

Is your feature request related to a problem? Please describe.
Well right now user cannot update SKipper right from app.

Describe the solution you'd like
Add option to settings menu "Check for updates" that would check for updates and offer downloading new version.

[JohnySeven]

On Linux:

sudo apt-get update
sudo apt-get --only-upgrade install skipperapp