Add a bunch of missed localization strings, update english and finnish to match.

src/App.vue

src/components/conversation/conversation.vue

src/components/friends_timeline/friends_timeline.vue

src/components/login_form/login_form.vue

src/components/post_status_form/post_status_form.vue

...ic_and_external_timeline/public_and_external_timeline.vue

src/components/public_timeline/public_timeline.vue

src/components/registration/registration.vue

src/components/user_finder/user_finder.vue

src/i18n/messages.js