Fixes #4, #7: Clean up the alignment of the navbar when in wide view.

Changes made:
- Style the code4hk badge with Bootstrap formatting.
- Ensure that dropdown is aligned relative to parent container and not absolutely positioned. Make sure that search form is left-aligned to avoid issues with invisible overlap blocking block events on code4hk badge.
- Move the margin from the container around the umbrella and "Solidarity with Hong Kong" text to just the umbrella.

Test plan:
Tested in Safari and Firefox Aurora again, like with the last pull request.