Using LTA slots to interpret time

The hdc_policy will now check which time is the last one talked about and search for directions or weather relating to that time.

LTA for departure_time also looks at (plain) time so that user can mix utterances like this:
1) odjezd v 5 hodin
2) za 5 hodin
3) v 5 hodin
4) odjezd za 5 hodin