Add option to add a device with a range of pixels (not starting from zero)

[42willow]

For example:
If someone wanted to have a long strip of pixels and wanted to make different effects for different parts of that strip then you should be able to create a device with pixels no.123 to no.456

I am cutting my strip and having wires linking the segments together and I don't want to have to use multiple data pins because that would make it messy.

[42willow]

Possible duplicate of #134 or #136