Timepicker accessibility

[gselderslaghs]

Proposed changes

This PR fixes issue as described in this comment in #476
Additional styling improvements have been applied as described in the Material guidelines, this applies mainly to margins/paddings, the addition of a button class to the am/pm buttons and usage of button-filled state instead of applying text-primary class on am/pm select

Screenshots (if appropriate) or codepen:

Before

After

Types of changes

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to change).

Checklist:

• I have read the CONTRIBUTING document.
• My commit messages follows the conventional commit format
• My change requires a change to the documentation, and updated it accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[wuda-io]

LGTM