Add option to set default preview state

[red-kite]

Simultaneously remove obsolete option for default live-preview

New tabs get additional triggerPreviewUpdate

[mitya57]

Thanks for the pull request!

I have changed the setting to be string, and changed the labels to be better readable.

Also I have added a line to make sure empty document is not created in preview mode. It has a drawback that if you set mode to normal-preview, and then open a document in the existing (empty) tab, it will be open in edit mode (since the createTab() method is not called). But we can solve it later if you want.

[red-kite]

Also I have added a line to make sure empty document is not created in preview mode.

Great thought! (already had this in my mind for another commit)
Your implementation works for New File but existing, empty files open in preview.

In window.py:

from os import stat

		#if previewState == PreviewNormal and not fileName:
		if previewState == PreviewNormal and (not fileName or stat(fileName).st_size == 0):

does the trick for me.

I could follow your mentioned drawback by opening a file from the menu in a new tab. I have never done this bevor. Think this is a very special case we can live with for now.

Thank you very much!

[mitya57]

I think opening existing, empty files is also a very special use case. And you can always disable preview for them manually.

[red-kite]

As I'm already using "Ask to create missing files #436" extensively this happens quite often. But for the current issue this doesn't matter. Close accepted :-)