Change Line Chart face X axis configuration to just a "history amount"
With the changes to have an API that determines what the update rate is for sensors, it now becomes rather awkward to specify the number of items a line chart should keep, since this number is dependant on the update rate. So instead, change the line chart to have a single configuration value indicating how much history to keep, in seconds. This is then converted to a number of items based on the current update rate of the sensor.
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