Display full application names under their icons

Until now all application names in the icon grid were truncated to a single line and then ellipsized (default behaviour of StLabel). This change removes the ellipses and instead wraps the application names across multiple lines if necessary. So you can now always read the application names in the icon grid.

When necessary, the hover highlight is heightened to surround the multi- line labels.

The apparent visible size of the icon grid to the user is unchanged.

https://bugzilla.gnome.org/show_bug.cgi?id=663725
https://launchpad.net/bugs/968213