Timezone dropdown and other improvements

[OliverBalfour]

Changes

• Timezone dropdown (requires npm ci, new dependency)
• Improve event colour contrast with white text
• Make Google Maps links visually distinctive
• Stop displaying week of the year
• Add development instructions to README
• Set initial calendar date to max(start of semester, current time)

[OliverBalfour]

Whoops made the PR in the wrong repo, sorry!