add better_errors gem
fix graph target browser #BUGFIX
preliminary "native" graphite widget #80 #104 #93

* select widget "graphite" to play with it
* uses more recent graphite-web SVG format API
* embeds SVG as-is (sets background to transparent)
* you can use all supported graphite functions

known problems:
* width/height settings are hacked together
  for a two column, 1 row graph
* the svg/css needs fine tuning 
* error handling needs improvements