Refresh: CSS base bundle clean up

[wen-2018]

Description

Currently, the m24 base bundle doesn't include existing component styles. We should update it to include common styles in protocol-mozilla, but with imports of the new nav / footer, home and new styles instead of the old ones, avoiding serving redundant styles to users when the brand refresh switch is on:

{% if switch('m24-base') and LANG.startswith('en-') %}
  {{ css_bundle('m24-base') }}
{% else %}
  {{ css_bundle('protocol-mozilla') }}
{% endif %}

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Tasks

Beta Give feedback

1. remove old navigation styles from the new navigation and its stylesheet (fixed in update nav to remove existing nav styles #15222)
2. add new nav and footer styles to the new base CSS bundle
3. remove old nav and footer styles from the new base CSS bundle
4. import styles of components that are used on all pages using the existing designs to the new base CSS bundle