add carrierwave gem

add carriervawe to Gemfile
generate uploader for picture in post
add migration for adding picture to posts

migrate schema adding pictures to posts
add public/ to .gitignore
remove coverage files from repo
fix coverage line in .gitignore
mount uploader to post model
add picture input to new post form partial
implement image representation in show post view
add picture to permitted attributes of post in posts controller
add translation for picture label