Vertical & horizontal layout : fix panes’ min & max dimensions

Correct the minimum and maximum dimensions for the NSSplitView panes respectively used for the article list and the article view.
Vertical layout : allow summary to expand more.

Only the summary column (used in vertical layout) should autoresize (to fit the available space)
Better dimension saving when switching layout

For when user switches from vertical to horizontal layout and vice-versa
Fix an occasional bug when switching view

When an articleView is recycled while switching from the unified layout to another one, the ArticleListView could receive a notification he couldn’t handle.
Clarify some comments
Merge pull request #326 from barijaona/verticalLayout

Fix panes dimensions in horizontal and especially vertical layout
Minor changes - tested OK in 32bit 10.6 and 64bit 10.10.