Provide a direct place to change the logo from Administration

Average time for "Change Logo" task, for beginner users, during our Scenario #6 usability sessions was 7minutes. This period is very high, especially for such a common task. This length causes abandonment and frustration. 

The issue we have is that we have several levels where the logo can be changed (ColorTheme, Skin, File system). New users are confused about Skin and ColorTheme differences, plus the logo change is hidden and duplicated for each of the possible ways. 

The proposal is to provide a direct place to change the logo from Administration, Look & Feel, Themes section. Read more about the proposal at https://design.xwiki.org/xwiki/bin/view/Proposal/IdeaChangeLogo