Chart support:
  - refresh_charts.py - create chart data cache
  - charts.html - list available charts and show specified chart
  - db.py - get chart data from chart cache
  - views.py - /charts and /charts?chart=<chart_name> support

Cleanup <script> sections. Base template includes common .js and .css links in <head>. Other templates include files only that they use
Blueprint 'ck': support chartkick.js from chartkick package. Chartkick.js from project static removed