Modify content rewards

[pmconrad]

As discussed with cob:

1. Remove curation rewards
2. Halve inflation - 20% of that to witnesses, 30% to VESTS, 50% to content
3. Distinguish full-time/part-time users (more or less than 1h playing time in last 24h)
4. Define play_time in streaming_platform_report_op to be in seconds, then put a cap on user's total playing time at 86400 seconds/day