#95 tree browser context menu is too long

[Adam Dingle]

The tree browser context menu is too long and is unwieldy to navigate. Here are some suggestions to shorten it:

- When the toolbar is visible, I think the context menu should not include commands that are available from the toolbar (Go up, Set path from document, Refresh).

- I personally think it's simply not worth having the "Close: <filename>" and "Close child documents" menu items. Up to you.

- You could consider moving "Show bookmarks", "Show hidden files" and "Show toolbars" into a submenu.