Add support for RTL feed content

template/common.go

template/html/bookmark_entries.html

template/html/categories.html

template/html/category_entries.html

template/html/category_feeds.html

template/html/common/feed_list.html

template/html/edit_feed.html

template/html/entry.html

template/html/feed_entries.html

template/html/history_entries.html

template/html/search_entries.html

template/html/shared_entries.html

template/html/unread_entries.html

template/views.go