Support auto scaling for y axis

[mwalliczek]

Currently auto scaling of the y axis is disabled for all entities with only positive values (see js/entity.js line 210).

However, for pressure given in hPa that makes the graphic more or less useless, because you would not see any difference between 995 and 1005.

So I manually enabled the auto scaling by setting the min value to "null", like this:

htdocs/js/options.js:
@@ -93,7 +93,8 @@ vz.options.plot = {
                },
                {
                        axisLabel: '°C', // assign temperature to 2nd axis- remove if not used
-                       tickFormatter: vz.wui.tickFormatter             // show axis label
+                       tickFormatter: vz.wui.tickFormatter,            // show axis label
+                       min: null
                },
                {
                        /*
@@ -103,7 +104,8 @@ vz.options.plot = {
                        */
                        position: 'right',
                        // alignTicksWithAxis: 1,
-                       tickFormatter: vz.wui.tickFormatter             // show axis label
+                       tickFormatter: vz.wui.tickFormatter,            // show axis label
+                       min: null
                }
        ],
        selection: { mode: 'x' },

and it seems to work. I would like to have this behaviour as configurable option - it this possible?

[andig]

Would be happy to accept a PR. It should cover the general case.