Pytradfri

Contribution by lwis

Re-add supported features (158, lwis)

Move timeout to I/O API (155, tazle)

146 (ggravlingen)
148 (Lakitna)
151 (Lakitna)

139 (Lakitna)
140 (Lakitna)
141 (ggravlingen)

- Adding constants (126, 129, 130, ggravlingen)
- Improve functionality around lamp value ranges (134, Lakitna)
- PSK handling clarification (136, Lakitna)
- Libcoap observer timeout fix (137, Lakitna)