Rename `update_server_branch.sh` script

Rename `update_server_branch.sh` script to the more generic
`update_site_branch.sh`.
Make `update_site_branch.sh` more generic

Update script to:

 * run `npm run build` instead of `grunt`
 * use the directory name provided as a command line argument instead
   of the very specific "dist" name
Update `CHANGELOG.md`
v0.2.0