Add Freeze support

[emgre]

Closes #319.

• Add support for IMMED_FREEZE (0x07), IMMED_FREEZE_NR (0x08), FREEZE_CLEAR (0x09) and FREEZE_CLEAR_NR (0x0A).
• The No Acknowledgment versions are available through the broadcast addresses
• Support qualifier all (0x06) and start-stop 8-bit/16-bit (0x00, 0x01)
• IOutstationApplication now must implement IDnpTimeSource, so it must be able to return the current time.
• When a freeze operation occurs, the current value and flags of the counter is copied to the frozen value (if it exists). The current time (returned by IOutstationApplication) is used as a timestamp.
• When a clear is done, the current time (returned by IOutstationApplication) is used as a timestamp for the counter.
• The UpdateBuilder does not have an update member function to update the frozen counters, since all is done automatically now.
• Manual freezing is available in UpdateBuilder, also in the C# and Java bindings.
• A new DefaultOutstationApplication is available and it handles basic time synchronisation with std::chrono::system_clock.
• The outstation demo was reverted (I had copied the TLS outstation by mistake...)