Track buffers opened by chase

[piraz]

Chase track buffers running a code from a source file, let's call it the original buffer, even better chased buffer.

Let's keep track of those buffers, and let them attached to the chased buffer.

Let's keep some behaviors attached between chased buffers and chasing(tracked) buffers:

• when chased is hidden, chasing buffer should be hidden
• when chased is displayed, chasing buffer should be displayed