One Click entry view how is implemented

• If you use the keyboard to focus an album, a later click on the focused album should bring up the entry view.
• The viewport scrolling behavior should take into account when expanding the entry view manually.

I introduced some work arounds myself, but I think the end result is a little clearer. Basically, the logic of the code is:

1. When the mouseclick callback is called for the first time, increment the click_count by one and add a timeout to the _timeout_expand method (old _expand_and_scroll). Each subsequent call to the mouseclick callback would increment the click_count by one.
2. When the _timeout_expand method gets finally called, it haves to check two things: that the clicked album is the currently focused album and that the click_count hasn't went up. If this conditions are met, then we are sure that this is a second/third valid click, so we proceed to show/hide the entry_view.
3. Before returning, we make sure to update the currently selected album and clear the click count.

To knock out the keyboard movement issue and the rapidly clicking albums bugs, I had to do a somewhat dirty workaround on the selection changed callback:

if selected[0] is not self.last_selected_album:
    if not self.click_count:
        self.last_selected_album = selected[0]
    else:
        self.click_count -= 1

I'll explain the inner if-else since it's pretty confusing: the not self.click_count allows us to detect that the currently selection change was made through the keyboard, and hence we should update the last_selected_album or else the next click on that album won't know that that click should behave like a "second" click. On the else branch, reducing the click_count achives to correctly ignore double clicks when they aren't on the same album, and fixes the rapidly clicking albums issues.

Finally, some other things I moved around/deleted/changed:

• I moved the expand & scroll behavior to the expander callback, so it would be available ot either second/third click gestures or manual expansion.