Uncheck button when AppChooser is hidden

Clicking on the button will toggle AppChooser, however when a user
clicks an application icon the window is hidden.
We connect AppChooser's visible property to the button's checked
property to uncheck the button when the window is hidden.
Make sure PATH is set

It's starthawaii's job to do it.
Implement hawaii-desktop-shell protocol in C++ plugin

Implement the hawaii-desktop-shell protocol.

Closes #14