#Angular: Offer "full screen" option in vertical preview mode

[runboxdave]

Unlike in horizontal preview there is no full width option in vertical preview. It might be a good idea to offer what might effectively be a "full width" option so that messages can be viewed in a bigger window at the click of a button.

[gtandersen]

Ref: https://community.runbox.com/t/is-preview-pane-only-way-to-view-email/748/

[gtandersen]

See also #690.

[runboxdave]

Just to add some more details to this. A lot of this is about preference.

Many apps attempt to use the screen space available and end up doing things the same way. Presumably their extensive research has shown them there is a clear preference and we shouldn't be afraid to give customers a familiar interface to make the transition to Runbox easier.

On a mobile phone the vertical option when holding the phone in portrait doesn't open full width which looks strange, almost like it is a bug. The vertical mode is ergonomically pleasing because things collapse on top of each other from the left and right making it very intuitive to know where your message list is and by extension of the idea where the folder list is.

You can drag the preview pane to full width and then it behaves nicely until there is some kind of reset of this parameter. Whether we want a button to make this resizing easier or we just open full width by default isn't really a big issue. I don't think anyone (or many) would complain about it being full width by default.

In landscape mode there is enough space to keep a condensed message list on the left.

The same can be applied to tablets although there is more room (literally) to do things slightly different if we want in the future.