We pass the pillars via the template engine context, this avoid the
need to load `map.jinja` from the templates themselves and recude the
number of `pillar.get` calls.

* openssh/config.sls (sshd_config): pass `sshd_config` in the
  context.
  (ssh_config): pass `ssh_config` in the context.

* openssh/files/default/ssh_config: remove `map.jinja` import since
  it's now in the context.

* openssh/files/default/sshd_config: ditoo.

* openssh/known_hosts.sls: pass `known_hosts` in the context.

* openssh/files/default/ssh_known_hosts: use `known_hosts` from the
  context instead of calling `pillar.get` several times.

BREAKING CHANGE: Minimum Salt version support is now `2019.2` in line
with official upstream support; also use of the `traverse` Jinja filter.

Closes #153.

* ssh_config: properly render host options (fixes #145)

* ssh_config: whitespace optimization (fixes #145)

Now ssh_config also accepts string-or-list options, for serveral
keywords.

put the ssh_config Host:* options in the defaults file so they can be overridden

This gives us the ability to define system-wide definitions for specific Hosts, and their options.

For example, with this in pillar:

```
# this is the place for host-wide SSH config
ssh_config:
  ...
  Hosts:
    # this simplifies cloning with custom params
    # eg: git clone my-git:foo/bar
    my-git:
      User: git
      HostName: git.example.com
      Port: 2222
```

This would add a section in `/etc/ssh/ssh_config`:

```
Host my-git
    User git
    HostName git.example.com
    Port 2222
```

Made a small change to reflect the default sshd_config