ssh: Add simple ssh configuration module

Added configuration module for ssh client.
Sets some basic settings and sets a general structure for the ssh
folder:

```
.ssh/
  |- config
  |- conf/
  |---|- config.ssh
  |----- hosts.ssh
  |- keys/
  |---|- id_*
  ------ id_*.pub
```

Config only refers to the files situated in `conf/` directory, while any
`hosts.ssh` configuration redirects to the correct keyfiles lying in
`keys/`.
Actual settings can be configured in `config.ssh` and this file is also
committed to versioning, whereas keys and hosts are not.

ssh/.gitignore

@@ -0,0 +1,8 @@
+### SSH ###
+**/.ssh/id_*
+**/.ssh/*_id_*
+
+**/.ssh/keys/
+**/.ssh/**/hosts.ssh
+**/.ssh/known_hosts
+**/.ssh/authorized_keys