Add preset links to main, combined and distant signals

This adds preset links instead of a notice, which makes it much easier to add zs2, zs3 and other signals to an existing main, distant or combined signal.

![ks_mit_links](https://cloud.githubusercontent.com/assets/5783139/5375218/c205d562-8067-11e4-919b-8d04bc4300fb.png)


Please note that this relies on the names of the signals, so when changing any signal names, the preset name attribute in the preset links also has to be changed.