New generation bStat

Version 6 is a complete break from the past, with a greater focus on the activity stream and less support for historical analytics. It is also strictly focused on posts, and has no support for tracking activity on pages that can't be resolved to a post ID.

The old tables are abandoned, and this code does not (yet?) have a migrator for any of the data in them. I'm really not sure if any of the old data can be migrated or would have value in the new plugin.

Current condition:
- Reporting is just a skeleton with some `print_r()`s
- Tracking works for me, but needs more testing
- The tracking JS needs review, and probably performance improvement
- I'd like to add click tracking to the JS as well