Make buttons better accessible on touch based devices

The buttons were a little bit to small to hit accurately, now they are a bit wider.
Move Buttons to own tag files

This way we have to write less JSP code. A few more elements are likely to be
moved to JSP files as well
Rework error rendering so we don't have an inline scriptlet
Move keyboard navigation help to main div
Convert HTML wrapping to a tag
Indent code a little bit, no other changes
Add support for red buttons to the button-tag

Also fix the wrong title being displayed
Sync styles between button and red_button
Rework how categories and feeds are displayed.

This causes way more load when rendering the page, but we get a better result. This
currently is work in progress as we will change the database format, but I'd like to
get rid of the settings before doing so.

Currently missing is deletion of feeds/categories, renaming feeds/categories, etc.