Give user ability to control the line colours on the graph

[damies13]

Is your feature request related to a problem? Please describe.
Give user a way to save, retain and control the line colours on the graph.

• When comparing test results from different runs it would be easier if the lines are always the same colour for the same value
• when testing reporter with image compare easier to test
• sometimes the selected colour is difficult to see / distinguish from another value, so user may want to change it

Describe the solution you'd like
This will probably need 2 parts:

• save the currently selected colours in the report / template
• add a colour picker button for the matching colour in the data table