Add a counter for number of files with locations missing/inaccessible

**Is your feature request related to a problem? Please describe.**
When we have many models accessed and files are missing/empty/inaccessible we should store that at the FCS level for Nexus and have that number easily accessible for types of files.
**Describe the solution you'd like**
Add a property/variable on the FCSFile class that has a count of how many of the files/include files are empty/missing/inaccessible.