feat(*): #868 - more thumbnail-related progress

- Simple EXIF parser for JPEGs to orient previews correctly
- Restrict size of previews via canvas, qq-max-size attr cue
- iOS & Android support (as well as all modern desktops)
- simple previews template
- reorg of provided default templates
- identify DataViews as arrays

TODO:
    - fix quality issues at some sizes
    - Identify previewable files before attempting preview
    - "not available" and "preview generating" stocks
    - API method
    - Allow thumbnail from server (url in response)
    - unit tests
    - docs

[skip ci]