use git to track the saved json

TODO:
1. check if S3 remote exists, if not go 2., if yes, go 3.
2. setup remote on S3 and push
3. pull or clone from S3 first before permforming file save
upload S3 by aws-sdk, but not carrierwave

carrierwave upload with an unique key for each file.
this will cause folder in S3 not in order.

local folder and key pairs need to be designed
add s3fs to test heroku mount s3
add fuse for s3fs
forget mount s3 on heroku; use jgit instead
add jgit
use Procfile to setup jgit at home dir
test jgit on heroku
read cloned repo on heroku
remove Procfile to test heroku
add back Procfile and add rails env
replace carrierwave by jgit wrapper

using jgit to push/fetch s3 is more efficient.
keep carrierwave for later usage, ex. user image upload
clone s3 if local file is lost due to dyno restart

parsing local file to load data has issue
to debug on heroku then
get sheet for local path finding

rename method load to prevent from overriding ruby kernel method
add empty data template for new sheet data load

to fix emtpy data sending error
destory local tmp dir also
no more fake data
rename path to name
show commit history along

TODO:
1. deal with user name
2. use java script to catch save_data action to update history