InsteonPLM binding: added support for multi-button devices (KeypadLinc 2487S)

Enhancements to the binding to support multi-button devices like the 2487S. This required adding parameters to command and message handlers.

This pull request also incorporates the modifications to device_types.xml from request #1769, and thus obsoletes #1769.

Note: changes to device_types.xml require a syntax change for items that bind to a mini remote. Since there are currently only two known users of mini remotes the decision was made to break existing .items files now rather than carry the legacy syntax (button=..) forward. Again, this pertains only to devices that use the button= syntax, which is currently only the mini remote.

The changes in this pull request have been tested on a fairly extensive set of devices.