qx contrib publish: allow overriding of version number

[cboulanger]

qx contrib publish at the moment increments the existing version number according to the release type (major, minor, patch ...). We should add a -V/--version option that allows to manually set the version number.

[cboulanger]

A contrib should have a demo, which allows to see what it does and could be used in unit tests for quality control. qx contrib publish will warn if there isn't one and recommend to add it via qx contrib init

[cboulanger]

More changes:

• qx contrib publish should also allow to enter a custom release message
• in the confirmation, add the release type (major, minor,...) to the confirmation message

[johnspackman]

This issue was moved to qooxdoo/qooxdoo-compiler#82