More persistent view settings

[cameronwhite]

• Remember the selected view filter (e.g. guitars or basses) for each file. This might be something to save in the file itself?
• Remember the zoom setting preference. This is more of a user or device-specific setting so we should probably just remember the last used zoom level in the preferences and use that for new files.

[cameronwhite]

#315 added shortcuts for zooming in and out, along with remembering the last zoom level