Focus moves from post content to tags when switching to preview mode and back

[vickychijwani]

Steps to reproduce:

1. Open a post for editing
2. Tap the content text field to show the keyboard
3. Switch to preview mode and back
4. Notice that the focus has moved to the tags field

This behaviour is annoying as it breaks the flow when writing a post: write something, preview, go back and make edits, preview, ...

[vickychijwani]

The new behaviour is:

1. Tap content text field and type something
2. Switch to preview mode, keyboard gets hidden automatically
3. Switch back to edit mode, cursor regains old position and keyboard pops up automatically.

Only little issue is, the keyboard pops up in step (3) even if it wasn't visible just before step (2). I think I can live with that for the time being.