Add TOTP seed request and storage; add TOTP generation functionality

- Change EnrollmentFragment layout to reflect new enrollment process.
- Tweak string values in string.xml to reflect new enrollment layout.
- Tweak layout of OTPFragment.
- Add permission and functionality to connect to the Internet.
- Add keystore.p12 for the app to treat as a truststore (for testing purposes only).
- Add TOTP generator code.
- Change EnrollmentFragment to update OTPItem, and store seeds in BKS keystore.
- Change OTPFragment to load seed from BKS keystore upon app loading, and from OTPItem from then on.