Accessibility - Aria labels for buttons

[e218736]

Issue
Issue #1718

This PR aims to solve some of the 'inconsistent button labels' outlined in item 2 of Screen reader in the issue linked above. E.g. Buttons with material-icons are announced by the screen reader as the icons inner text. The announcement is often not indicative of the action performed by the button and can include announcements of 'underscore'.

Code changes:

• aria hidden applied to inner icon elements of button so that text isn't announced by screen reader
• Aria labels added to buttons which are descriptive of functionality

User-facing changes:

• None visible
• Screen reader announces descriptive aria labels on button focus

To replicate:

• With a screen reader active Tab to buttons above recipe/input/output and favourites button
• Expect screen reader to announce appropriate button functionality rather than icon titles