Show search button on left side of logo on mobile

<img width="423" alt="bildschirmfoto 2017-07-27 um 21 54 01" src="https://user-images.githubusercontent.com/7313617/28689510-25889784-7316-11e7-85d0-fd26f6e23885.png">

This goes together with #30, I suggest blocking the "hide search bar" behaviour on viewports with sufficient width because it causes confusion. 