Linking x-values of line plots with correspoding values on x-axis and probing for active sensor

I succeeded in probing for the active sensor (in my opinion this is the best guess that can be made) by comparing max and min value of a sensor within the last 24h.

The code sets the first sensor with different min/max values as active sensor. Other things that came into my mind were building means or merdians of all active sensors, but I really think that we should work with tabs here (e.g. mean temperature, temperature of T1 and temperature of T3 sensor) before implementing that.
I am not that experienced with highcharts to implement that, so I am just probing for the first active sensor and showing data of that sensor.

I also implemented x-axis linkage of the values (so they do not need to be in fixed intervals of one hour). This can be done by giving a bit more information to the highcharts api (datetime and value and deleting the pointInterval attribute).

I really think that these small changes make a difference and increase the usability of rnexus (since it should work now after installing following the readme instructions)