Pane widths change when moving between views

[mfid]

When moving e.g. from Inbox to Drafts folder, or to Plugins section, and then back to Inbox, the panes revert to default width, changing the way messages are presented. Image attached because it's easier than trying to explain with words.

[bengotow]

Merging in #97, #243

[natemhanson]

+1

[iamhenry]

+1

Very annoying.

[hirozed]

+1 It would be great if N1 could remember the pane width even after the app is closed. I have to change the width every time I launch the program.

[jstejada]

merging into #833