Add here to window config

[jmks]

Potential fix for #70

I've added a here option to the window configuration. It allows me to specify which window will replace the window invoking the itermocil command.

I manually tested this out with this layout file:

windows:
  - name: one
    root: ~/
    layout: main-vertical-flipped
    panes:
      - commands:
          - echo "w1 p1"
      - commands:
          - echo "w1 p2"
  - name: two
    here: true
    root: ~/
    layout: main-vertical-flipped
    panes:
      - commands:
          - echo "w2 p1"
          - echo "this should be the terminal that executed itermocil"
      - commands:
          - echo "w2 p2"

My python is probably not that pythonic, but rather more Ruby-ish 😃

[uloco]

Any reason, this feature isn't merged yet? I really find this useful ...