Adding a object interface to __salt__ & __pillar__ (pyobjects)

This is another suggestion from @mgwilliams. It adds an object to the
sls file scope named Salt, which dispatches its attributes to the
`__salt__` dictionary.

For example, the following two lines are functionally the same:

    ret = Salt.cmd.run(bar)
    ret = salt['cmd.run'](bar)