Return a list of included sites

[AugustT]

The returned object from an occupancy model should have the names of the sites included (after filtering by nyr)

@GPowney and @JackHHatfield91 to discuss

• [x] Identify where in the code the list of sites can be found
• [x] Add this to the returned object at the end of the function
• [x] This is very closely related to #45 - So do that issue while you are here

[AugustT]

@FrancescaMancini have a look at #45

[FrancescaMancini]

All done