Add functionality to draw multi-series column chart

See merge request !7

It is assumed that this chart type will be used for visualizing
aggregated results

Improve logic for performing basic aggregation

See merge request !6

Add functionality to draw multi-series line chart

See merge request !5

Add logic for performing basic aggregation

See merge request !4

Update scatter plot chart

Further improvements to logic for drawing scatter plot chart

See merge request !3

Update scatter plot chart

Improve logic for drawing scatter plot chart

See merge request !2

- Move the function within the module file

- Add documentation to the function

Currently, this function is only available in the scope of the
function that formats observations for the scatter plot chart.

Remove the missing observations from the first (larger) array.

Currently, this function is only available in the scope of the
function that formats observations for the scatter plot chart.

Get the index of the observations that are available in the first
array but are missing from the second array.

Currently, this function is only available in the scope of the
function that formats observations for the scatter plot chart.

Get the timestamp of the observations that are available in the first
array but are missing from the second.

The function paramaters are two observation arrays which are responses
from a SensorThings API instance.

The logic of the function is based on the premise that the first input
observation array is the larger of the two.

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