Make it so panel remembers changed width

[PrefixCoder]

Initially, the outline panel takes exactly half of editor's space.

One can easily make it smaller, like this:

But the moment pane switches off-on, or a different notebook is selected, it's width snaps back to half the editor

[skymagician]

同问。还有窗口最大化或者取消最大化的时候，目录栏不会跟着调整，还要再拖一下才行。

[chronos1970]

+1 for a solution to this issue

[youralmight]

We'd better add a variable Width: fixed, compact, or remember last width. Any way, this pane occupies too much space.

[cqroot]

The width of the panel cannot be adjusted using CSS. I haven't found a good way to fix it yet.

[manuerwin]

Can this be closed as a duplicate of #45 ?