Added a module to configuration the main link (MainLinkConfigure)

Configure the behavior of the main link on click.

### Options
* Action
  - open the main link
  - open the comments
* Focus
  - open in foreground
  - open in background

### Testing
Fully tested on Firefox and Chrome. I appreciate any feedback for about its behavior on other browsers.

### Other
* This is similar to the Single Click Opener module, but I felt it was different enough to warrant its own module.
* The module is disabled by default.
* My motivation for making this is the desire to only open the comments (since I can get to the content from there) and to have interaction remain as close to the normal flow as possible (left-clicking on the main link).