Language and file name

[AlexeyAnshakov]

Add input field above main edit container. It's going to be an input for json-ld file name. Use name from first title in Edit container. E.x. if
user type

My first article
Blah-blah-blah...

We must get

My_first_article

inside name input field. User can change on his own name if he would like to.
Must be checked for uniqueness and show error if we already have a file with the same name.
Add next (at right side of name field) a language dropdown. There must be only "En" for now.