Bugfixes, improve reader mode and ctrl+0

[tmarkov]

This PR contains 2 things:

1. Bugfix: In onCreated, only set zoom to default if it's 1.
2. Reset zoom to default every time it's changed to 1.

• This fixes some glitches with reader mode and allows ctrl+0 to sent to default zoom
• To be able to set zoom to 1 manually, the user can edit toolkit.zoomManager.zoomValues and change the 1 to 0.99 or 1.01.

You shouldn't merge both this and #8, I'm putting all my changes in one PR because I simplified the code a bit as well.

I won't close #8 in case you don't like the additional changes and want only the bugfix.