seabbs/getTBinR: Presentation mode

• Switched dashboard to default to 2018 data.
• Added a new WHO inspired {ggplot2} theme (theme_who) and colour palette (who_palettes) resolving issue #86. Plus scale_colour and scale_fill_who functions for using the palette. Thanks to @mariabnd for implementing this.
• Added a new function - for_presentation - to switch plots to presentation mode.

• Additional testing and examples to support the new WHO inspired theme and colour palettes.
• Additional documentation for the new WHO inspired theme and colour palettes.
• Updated the spelling of organisation to organization in all uses relating to the World Health Organization. Thanks to @mariabnd for spotting this.
• Added @mariabnd as a package contributor.
• Changed verbose to default to FALSE package wide.
• Bumped data availability to 2018.
• Standarised legend to be bottom aligned across the package.
• Dropped tidyverse from suggests as per this issue.
• Fixed legend types as per this issue

Thanks to @mariabnd for contributing to this release.