GUI Tweaks

[vkbo]

Mostly minor improvements to the GUI:

• When clicking enter on an item in the project tree, the focus remains on the tree and don't switch to the editor like it does when you double click. It makes it easier to flip through files and look at them by pressing enter repeatedly.
• For some fonts (especially Ubuntu) the minimum column width in the tree widgets would be estimated to be too large. It especially ment that the include when exporting flag had a column much wider than it needed to be. This setting is now overridden with the known size of the icon, plus a 6 pixel margin.
• Added a title icon and document icon to the outline view.
• Regrouped the options on the Build Novel Project tool a bit. They are now sorted into Titles, Format, Text and File categories, with more consistent labelling.

Source code changes:

• Renamed a few files with long file names to something a bit shorter, and made the naming of files and classes a bit more consistent. This also reduces the width of the logging output by 10 characters.
• Replaced the hidden handle columns in the project and outline trees and used setData instead. The columns were originally there for debug purposes, but haven't been needed since the tree view was first designed.