Improve space for library names on the left

[MikeMitterer]

Library names will become longer and longer as Dart and its number of libs improve. As you can see in my SS I'm using the .. _{naming convention. It's hard to recognize the second level but if there is a third level like with mobiad_rest_ui_mdl.services.localjob there is no way to choose the right lib from the left menu without try and error.}

[jcollins-g]

@devoncarew I think your changes address this?

[devoncarew]

I'll add a bit more space for the name, but still have the same issue with really long names.

[sigurdm]

Our ui looks a bit different today. And libraries are now mostly named with the file name. But the point still kind of stands.

We could find a way to show the entire name on hover (either as a tooltip or above the pane).

We should think about alignment with pub.dev and how space is divided on the page