Directory: Create periodic snapshots of specific stats for tracking over time

[coreymckrill]

Pulling this issue together from a few other places, mainly this comment.

The idea is to keep track of a few key stats (listed below) by generating a "snapshot" post containing the stats numbers at that particular moment, very similar to how it's done on the 5ftf site.

Open question: should snapshots be generated daily, weekly, or monthly? The 5ftf stats are bi-weekly, but things are likely to change more often on the Pattern Directory, so daily might make the most sense here.

Initially, the stats to track are (list subject to change):

• Total number of published patterns
• Total number of unlisted patterns
• Total number of favorites
• Total number of flags, any status (reported patterns)
• Total number of pending flags
• Total number of resolved flags

We could also grab some other related stats, such as:

• Total number of patterns with at least one favorite
• Pattern(s) with the most favorites
• Total number of patterns with at least one flag, any status
• Total number of patterns with pending flags
• Total number of patterns that have reached the flag threshold and have been set to pending status for moderator review

Once frontend pattern creation launches, we might also want to see things like:

• Total number of published patterns for each category
• Total number of users who have at least one published pattern
• User(s) with the most published patterns
• User(s) with the most flagged patterns