Renaming generic fragment-hosting layout.

- Renamed layout XML from activity_crime to activity_fragment.
Creating an abstract Activity class to host a Fragment

- Refactored generic code from CrimeActivity into a new abstract class SingleFragmentActivity for code re-use.
Changes meant to be incl with previous commit!
Updating app to work with a list of crimes.

- Updating model layer from a single Crime object to an ArrayList of Crime objects stored in a singleton CrimeLab class.
- This list of crimes will be shown in a new activity CrimeListActivity (which uses a new fragment CrimeListFragment).
- Adding string resource for the new activity title.
- Updating the manifest to declare new activity CrimeListActivity as the launcher activity.