Create a temporary function that wraps the scatter plot drawing logic

... from multiple datastreams. Its single parameter is an array of
strings representing the building, sensor and sampling rate.

Retrieves metadata from an array of Datastream URL strings

Add parameters to function that hold information about the two series.

Remove hardcoded arrays used for testing.

Add weather station information

Add bare bones scatter plot chart

See merge request !1

Add a blank line between the properties of the options object, in an
attempt at improving readability.

Initial approach at generalizing the function by extracting constants
from the options object of the scatter plot chart.

Add the basic structure of scatter plot chart

`Range selector` is analogous to the `zoom` of a chart. Set it to
display all the available observations from a datastream.

Returns the abbreviated versions of building IDs, phenomenon names
and sensor sampling rates

Returns the values of the currently selected options in the linked
drop down lists

Also, add HTML for third dropdown list

... based on the selection in first dropdown list. Functionality based
on a new `hidden` CSS class

Create parent `<div>` elements for both dropdown lists. In addition,
attach a barebones event listener to the new dropdown list

Get the max and min values of the heatmap color axis dynamically.
Fix the tooltip text for `null` observation values.

Deactivate datastreams that do not have observations

Formats datastream metadata for use in both linechart and heatmap

Add parameter for datastream metadata to function that draws line chart

Fetch datastream metadata together with the observations

Add parameter for datastream metadata to function that draws heatmap
chart