Display path of current source file in header bar
Currently, the full path of the current source file will be displayed.
This usually results in long path. When the path can't be displayed fully in 1 row for whatever reason (the window is resized, not enough space from the beginning,...), after a Ctrl-L (hotkey for redraw screen), it will wrap automatically, creating more rows as needed.

We have multiple options to resolve this:
- Leave as is
- Only display the filename
- Calculate the length of the string somehow (from
shutil.get_terminal_size(), for example) - Let user decide in config file
- Other....
Let's discuss this
fixes #170
I updated it to calculate the path string automatically to fit on 1 line
Currently, path will be updated if the user executes the next line of code by pressing n, s, c in the Source window(every time DebuggerUI.interaction gets called). Ctrl-l to redraw will only redraw the current path. I don't know if it's possible for Ctrl-l to update the path as well.
A thought on this: an optional footer might be a better place. The header currently displays very useful information that helps new users get started with using the debugger, and I don't think we should lose that.