reimplement charts with nv.d3

ugly but basically functional (no brush & link yet)
scatter chart for numbers, some formatting fixes
line chart for dates
exclude undefined x values that kill my charts
implement time series as line chart

- default bin granularity: days
- TODO: let users control time granularity
- use bars for dates and numbers, no scatterplots
clean up tooltip and axis design
rename 'word frequencies' to 'metadata profile'
make sure date value is a string
add date granularity selector (default only)
add user control for date granularity
fix bug in date sorting for timeseries
sorting dates in the wrong place
fix widget sizing
bring NV.D3 css into source control
don't let nvd3 eat all the SVGs
Merge pull request #70 from Wordseer/new-word-frequencies

New word frequencies implementation