Use lato font by default

as per UX

debian/control

@@ -16,6 +16,7 @@ Architecture: any
 Depends:
  ${misc:Depends},
  ${shlibs:Depends},
+ fonts-lato,
 Description: Simple Wayland shell
  Phosh is a simple shell for wayland compositors speaking the
  weston-desktop-shell protocol.

src/style.css

+.phosh-panel {
+    font: 15px lato-regular;
+}
+
 .phosh-panel-btn-top-left {
     background-image: none;
     border-width: 0;