coin2html: add balances chart

[mkobetic]

Use a treemap to show balances of selected accounts at the To: date. Uses SVG title element to show a tooltip with the details, useful when the details get clipped due to the rectangle being too small. Clicking on the rectangle makes the corresponding account the currently selected account.

Also fixes:

• default the aggregation granularity based on the selected time range (the weekly default was annoying for larger time period)
• also adds title element to the register chart to get the details tooltip on hover.