Albert v0.15.0 released

This release increases the required versions of the dependencies to Qt 5.9 this means that some distributions will not be supported anymore.

Major changes:

• Fancy usage graph in the settings
• QML frontend: History search of the input now allows substring matching (Type and navigate)
• QML frontend: Store user input of every session
• Add extension “Fortune”
• Add extension “Window switcher”

Further the release contains minor changes and fixes.

Check the git log for details.