Drop opinionated settings for PWA

* Base URLs are set to / in PWA's default settings anyway
  * With https://github.com/silviolleite/django-pwa/pull/32 merged, the defaults will
    work under all circumstances without changing settings
* l10n/i18n assumptions should not be made. PWA will see another MR to enabled
  it to use the language settings used in Django

Closes #140.