Make update check non-blocking

[Pidgeot]

Here a user describes:

If the device isn't connected [the PyLNP] seems to hang for about a min or two and then throws an error when the connection timeouts -- you can ignore the error and the pack works properly but the delay gets a bit annoying after awhile.

Adding an option to disable update checking would be a viable if inelegant fix - though still desirable from eg a privacy perspective.

Making the update check non-blocking would be a cleaner resolution of this issue. If an update was found, it could interrupt to pop up a notification; if no update was found or the check fails it passes silently.

[Issue created by PeridexisErrant: 2014-09-18]
[Last updated on bitbucket: 2014-09-19]

[Comment created by Pidgeot: 2014-09-19]
Perform update check in separate thread (fixes #25)

→ <<cset 8af740bcaa20>>

[Comment created by Pidgeot: 2014-09-18]
Agreed, this is definitely something that needs to be done.