Open first unread post by default on topic with unread posts

prosilver does currently come with a small icon to click onto to get to the first unread post of a topic. With a desktop client this is usually fine to use. However, it's cumbersome to use with touch due to its small size. In addition to that, most often users just want to see the first unread post so there is a high chance of click and miss.

Instead, we should be defaulting to opening the first unread post when clicking on a topic with unread posts.

View on search page (also base for viewforum etc.):

General changes:

• Removed unread icon
• Unread topics are highlighted by bold text and colored icon

Another example from viewforum: