DUI: SearchBox, LibraryButton.

# Preface
Once it was such PR(about centering SearchBox), but after all these movements from one fork to another changes were lost somewhere. So, I have added them and also resolved one more bug.
It occurs, when user click on LibraryButton. Since we have now MinWidth of LibraryView it causes some problems, look at pictures.
# Before
![image](https://cloud.githubusercontent.com/assets/8158404/4186905/f064fb3c-3764-11e4-81a7-644961bf2901.png)
# After
![image](https://cloud.githubusercontent.com/assets/8158404/4186874/a883fc82-3764-11e4-977c-c2e318bbc812.png)
# Solution
I've added `OnCollapsedSidebarClick` to revert our changes of making LibraryView visible.
# Reviewers
@Benglin, please take a look.

Link to YouTrack:
[MAGN-4510 DUI: "Library" label is not moved to left side after clicking to Library expander](http://adsk-oss.myjetbrains.com/youtrack/issue/MAGN-4510)
Much better name, thanks!