Add column settings for project and novel tree

[vkbo]

Based on discussions in #1351

It would be useful to add a "Column Settings" tool to each of the tree views so the user can customise the columns a little more, including scaling them. Options for sizing would be to set a max size for each column, and be able to choose which columns gets the remaining space.

At the moment, the title column gets the remaining space in both trees, and the optional third column in the novel tree is hard capped at 25%.

[vkbo]

The novel tree already has customisation options. However, one that can definitely be added for the project tree is the option to show document header instead of item label for all documents that have a header. See #1443.