Add some additional functionality

[brenca]

Added hotkeys

• Ctrl/Meta + Scroll to Zoom
• Ctrl/Meta + PageDown/PageUp to always jump a whole page
• Ctrl/Meta + Alt + w/p to force fit-to-width and fit-to-page

Added url parameters

• view: fitW/fitP - uses fit-to-page or fit-to-width on load (standard open pdf parameter AFAIK)
• toolbar: 2 - added the 2 value that makes the toolbar visible, but doesn't include empty space for it at the beginning of the document

[brenca]

Fixed! 👀

[brenca]

@kevinsawicki :eyes:

[kevinsawicki]

Thanks @brenca, pulling into Electron via https://github.com/electron/electron/pull/9892