Check for Update - feature request

Feature Request:

To facilitate running on the most recently released version of scancode-toolkit, add "Check for Software Update" under Help menu. Or some similar implementation. Without this it is too easy to continue running old versions because if you aren't actively involved in development, you probably don't go to github to check.

[pombredanne]

@bobgob1 excellent suggestion... I think we can use something such as the pip nag that comes this way as a simple warning message that is issues no more than once per week.

You are using pip version 18.1, however version 19.2.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.

https://github.com/pypa/pip/blob/449d268b5a6a6e126e4f00f0c848f101e689c2a0/src/pip/_internal/utils/outdated.py

Actually we already have code in a branch in 200d961 by @jdaguil so it should be easy to update and activate!