add "upload" functionality and "replace" functionality

Created by: liyakun

Functions to add new file to current repository and replace the existing file in current repository are added.

Update show.html.haml

add 'upload' view

Update _tree.html.haml

add 'upload' button

Create _upload.html.haml

show upload window

Update file_action.rb

allow user to upload both base64 file and text file

Update _actions.html.haml

add replace action button

Update show.html.haml

add replace (update) view

Create _update.html.haml

show update window

Update CHANGELOG