[tempus2016]

A new history style, column: vertical columns over time, for energy used per day, rain per hour or hours of heating per day. It uses the shared history frame, so periods, previous/next, statistics, axes, the tooltip and the compact layout all work as on the line chart.

It is set up to be right with no options. With no period it shows the last 7 days; with no group_by it picks a grouping for the span (hours up to two days, days up to two months, then weeks, then months; today by hour, a week or month by day, a year by month); and with no aggregate it shows how much a meter went up (change) when every entity is a meter (state_class total or total_increasing), else the average. So an energy meter on its own draws a column of kWh per day. group_by: none draws one column per reading.

• Rounded outer ends (rounded, on by default). Columns are drawn as HTML over the plot rather than in its stretched SVG, so corners stay round.
• labels puts each column's value on top (a stack's total), and hides them when the columns are too narrow to fit them.
• stack: normal piles series up; stack: percent scales each column to 100 %. Positive values stack up from zero, negative ones down.
• Negative values hang below zero, and the axis always includes zero.
• color_by: bands colours each column by its value's colour band.
• range: true draws each column from the group's lowest to its highest, with the average marked across it. From statistics it asks the recorder for min and max; from history it takes the spread of the values held in each group. The shared history frame gained an opt-in for this, so other charts are unchanged.
• Several entities sit side by side in each group.
• An entity's target (from the Limits section) is marked across each of its columns.
• When grouped, the time axis puts one label under each set of columns (Mon, Tue... or 26 Oct, Oct, Nov), every second or third when they would not fit, and the tooltip names the whole group ("26 Oct - 1 Nov") and highlights it.

Editor: Chart section has the period (7 days by default), Group readings by (with Automatic and Don't group), Combine with, Stack, Colour, Range, Show values on the columns and Rounded tops, then axes and layout. Each entity gets its own Colour.

Part of milestone 1.3.0 (tracker #47). Tested on the dev Home Assistant instance.

Closes #11