revise error message to English
add session read record interface
display new flag on unread message
consume read flag on front end
fix history interface by add prefix h_
fix history topic prefix issue
refactor to scala style
setup functional test of importing
use real data for importing test
add batch creating for children history
add employee importing test
refactor to move ws helper metheds
initialize history web pages
display multiple images in history
allow to delete one message or history record
allow upload multiple image in history
display n/a when no content in conversation
add limitation of uploading history record images
use qiniu image option to optimize the image size
use formal empty html tag