Option to Replace files in Web IDE
Spinoff from https://gitlab.com/gitlab-org/gitlab-ce/issues/44845#note_72643404 .
TLDR: Have a replace option for files, which basically does delete+upload. This is useful when we want to replace binary files like icons, images. Usecase: I want to change my website's favicon. I can do it in one go using "Replace" instead of doing delete and upload manually.
/cc @dimitrieh @jramsay