Increase the amount of information available in the sidebar and customization options

[Mrnofish]

I use Fluid Reader every day, it's the best reader I could find. However, there are some key areas that could use some improving:

• Making the sidebar resizable so that it can be adjusted to the feed's average title length and screen size
• With a larger sidebar, displaying additional information such as author or categories. Author's name is the most important field for myself personally, but the best solution would be to have per-feed settings to turn on and off the display of author name and categories.
• Allow customizing the font for the sidebar (size and font, e.g. one could select a narrow bodied font). Partly related to #347 but more general.