Feature/optimisation

[ahosgood]

Changed

• Renamed "files" component to "files list" (files -> files-list, tnaFiles() -> tnaFilesList())
• Renamed "featured records" component to "records list" (featured-records -> records-list, tnaFeaturedRecords() -> tnaRecordsList())
• SCSS mixin colour.light changed to colour.always-light
• Index grid items within contrast blocks are now accented
• Colour variables --button-accent-text and --button-accent-background have changed to --button-accented-text and --button-accented-background
• Colour variable form-error split into form-error-border and form-error-text
• Moved the grid component to utilities

Deprecated

• Removed colour.plain SCSS mixin

Removed

• Removed search filters component
• Removed sensitive image component
• Removed width: 100%; from reset of <video> and <canvas> elements

Fixed

• Incorrect aria-labeledby attribute changed to aria-labelledby in gallery items
• Add better labels for buttons in gallery component