Allow tabs to be shown on multiple line when they don't fit in the available width

When lots of tabs are added and/or the width of the Glimpse window is reduced, some tabs were hidden from view. Also sometimes the right-most tab would be partially hidden by the Ajax and History tabs.

Removed the fixed height of .glimpse-tabs so multiple lines of tabs can be shown.

Added 120px padding-right to prevent the tabs inside .glimpse-tabs-instance being hidden underneath the Ajax and History tabs