help-box-spike: moved ToolTip next to settings icon

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I think #65 look good, but thought it might had been easier to show my suggestions then describe it etc..

• moved the How Does this work next to settings and keyboard shortcuts, this saves the extra line in TimedTextEditor.
• because after moving the tooltip the black background didn't quiet work with the background of the MediaPlayer / PlayerControls area, changed it to background colour of the keyboard shortcuts, better colour scheme match, readability, consistency etc..
• moved some of the CSS properties to the props of the component.
• as refactor, to keep things tidy, I've noticed that the ToolTip component has a list of CSS properties it takes as props, might be good to make use of those as much as possible and add extras only when there might be shortcomings.

Let me know what you think

[pietrop]

Also see this note for some possible future work outside of the scope of this PR https://github.com/bbc/react-transcript-editor/projects/1#card-16169755

[pietrop]

disregarded in favour of #65