Don't error if device switched off

[brianmay]

Previously get_device or the related functions would retrieve a list of devices that it contacted in the last x seconds. Then we would contact each light in turn to try and apply some sort of filtering.

This would error out if the light had been switched off.

This patch attempts to contact each light and skips it if it cannot be contacted.

Closes #6

Note: I haven't tested this latest version just yet. The previous version, which was similar worked fine. Will do that ASAP.

[brianmay]

Looks like my change breaks things, will debug tomorrow.

[brianmay]

Have updated the patch. Can't use filter as the name of the parameter, as it overrides the Python filter function.