created mergedConfig getter to avoid obnoxious checks for undefined everywhere

src/components/favorite_button/favorite_button.js

src/components/favorite_button/favorite_button.vue

src/components/post_status_form/post_status_form.js

src/components/retweet_button/retweet_button.js

src/components/retweet_button/retweet_button.vue

src/components/status/status.js

src/components/user_card/user_card.js

src/components/user_card/user_card.vue

src/modules/config.js