Allow salt modules to be refreshed on demand.

As an example for the above feature:

```yaml
python-pip:
  cmd:
    - run
    - cwd: /
    - name: easy_install --script-dir=/usr/bin -U pip virtualenv
    - reload_modules: true
```

See the last line?
If no exception occurs in this state, after it's execution, salt **will** reload it's modules.
Add documentation about explicit module reload on states.
Merge pull request #6858 from s0undt3ch/features/states-reload

Allow salt modules to be refreshed on demand.