[PoC] Cronjob based Hashrate graphs
[FIX] Skip stat storage on missing data
[REFACTOR] Use raw statistical data
[FIX] JS compatible time field
[REMOVE] Debug output
[UPDATE] Use 24h range for account based graphs
[UPDATE] Removed noticable markers, removed both graph
[ADDED] Flush statistics_users entries after 7 days default
[UPDATE] Overhauled graphing stats

* [REMOVED] Pool/Combined hashrate graph until we have a proper SQL to
  generate this data. Volunteers?
* [ADDED] Worker and share rate statistics over time
* [ADDED] Admin setting to change graphing days (default: 1 day)
* [ADDED] Purge entries older than admin setting
* [REMOVED] Template files that aren't used anymore
[CHANGE] Shares/s to diff1 shares/s
Merge pull request #2281 from MPOS/graphing-refactor

Graphing refactor