Improve keyboard navigation and integrate preview in main dash

Dash has quite a powerful search and the preview with actions is helpful but could be extended. But preview is not intended for keyboard navigation. There is no useful or any keyboard combination to open the preview and return to search pane.

So I suggest either integrate the preview beside the search pane (above search textfield, below left results like now, expanding to the right for preview) or at least provide keyboard navigation. Currently preview open needs mouse, ESC at least returns to search but focus is not on previously previewed item any more. I would prefer the first solution, but I admit it is a bigger change and would probably need more discussion.

To make the previews really useful for advanced users, I would add some simple but powerful actions:
- All file system items should have an action for copy path / filename.
- Folders should have an action for opening parent folder, secondly opening a command prompt on that directory.
- Textfiles should display the first lines of text as the preview.

Furthermore, I would be willing to help implementing some of these features. Especially adding the actions should be possible without too much pain.

Implementing keyboard based filtering would be great too. For example, too type cat:Apps for only display applications and so on. With all these features, dash would be mature for users favoring keyboard over mouse.

// EDIT: Here a gimp manipulated image, how I would integrate the preview: http://snag.gy/IpKsW.jpg