Small Fixes

I've had a look at some of the recent changes, great to see so much progress. This branch adds some very minor fixes for things I noticed:

Typo

Fixed typo in the menu (the string is not yet part of the translation files)

Screenshot viewer controls

In analogy to the maplist and serverlist, I've added the possibility to open screenshots with LMB and space.

Arc notification

The arc kill notification still uses the hlac image, I've updated it

Slider direction

Currently, mousewheeldown and the PgDn key move the slider up, while mousewheelup and the PgUp key move the slider down. This doesn't make sense, so I've inverted the controls.

Scrollbar thumb minimum height

The scrollbar image is subdivided into 3 segments with a ratio of 1:2:1. While the middle segment is intended to be stretched, the outer segments are not. The current minimum height for the scrollbar thumb is 1*width, causing the thumb to be cut off, as seen in the advanced settings dialog. I've changed the minimum height to fully include all "unstretchable" segments.