Rename chef.erb to secret_key.erb.

chef.erb is now template for generic SSH secret key,
so rename it to show its proper role.

This commit refs #219.
Add and consolidate the SSH databags.

This commit refs #219.
Generate the SSH secret key, by retrieving data from databags.

This commit refs #219.
Deploy SSH configuration file.

SSH configuration file contains:

- bitbucket.org settings
- github.com settings
- other server settings

This commit fixes #219.
Merge branch 'id/219' into dev