Speed up scrolling with up/down keys

This commit reduce time spent on IconProvider::getIcon and misc::parseHtmlLinks to almost zero. Before these commits:

![up-down](https://cloud.githubusercontent.com/assets/286877/4967090/2ada95a2-67f7-11e4-903d-84cfcb693db4.png)

After:

![up-down-opt](https://cloud.githubusercontent.com/assets/286877/4967095/8e7397f8-67f7-11e4-8918-8d464878a74f.png)