Cleanup, fix refresh, and add openPosition setting

[mbudnek]

These are the changes I've made to my local copy of this driver. The main points are:

1. Clean up formatting
2. Fix the refresh command to work properly if the "reverse direction" setting is enabled
3. Add an "open position" setting instead of using a global, hard-coded value
4. De-duplicate a bunch of code and use a single setLevel method for all position control
5. Port the battery level refresh code over from the smartthings driver