Add low level code for sftp service
Implement SFTP service API.
Merge branch 'master' into issue#320

Conflicts:
	src/rockstor/prep_db.py
	src/rockstor/smart_manager/urls/services.py
	src/rockstor/system/services.py
fix regex match in sftp service check
Add rockstor sshd_config template
low level stub code for ssh config manipulation
Add SFTP model
Add SFTP api stub code
update sftp model with share one-one field
log the exception string in handle_exception
add share validation helpers and put them in separate file
Add system level sftp support.
Get validate_share from share helpers
Implement sftp api
update buildout and settings template for sftp
Add cli support for sftp
Merge branch 'issue#320' of https://github.com/schakrava/rockstor-core into schakrava-issue#320
Front end support for SFTP

Modify sftp model and serializer to add share name in serialized data
Add templates, views and routing for sftp pages
Add handler for delete
create one extra directory level in sftp mount path.