Resized images

[tobiasKaminsky]

What it does, copied from ownCloud and heavily discussed there, so here just a CR:

• Clicking on an image loads a reduced version to the cache.
• The width and height is determinated by the screen.
• the benefit is a very small, but yet usable preview of the image.
• it can be used to send via whatsapp, or as a file to another app (like k9) with the correct filename.
• resized images are not treated as downloaded files. If the user wants to have the real file, he has to long-click and select download.
• clicking on an image shows first a square thumbnail (if available) until the resized image is loaded

ToDo

• test with disabled API (gallery app)
  • test if thumbnails api can be used -> not possible right now
• Unsupported image formats Resized images owncloud/android#1599 (comment)
  • svg
  • tiff
• Bad preview of landscape images Resized images owncloud/android#1599 (comment) [WIP]
• sharing a non-downloaded image on Android N fails (at least with whatsapp)
• sharing a non-cached resized image fails -> first download resized version
• a resized image should load immediately (first on queue or dismiss all other current downloads)
• download of a resized image also with a nice download animation on the bottom?
• snackbar is sometimes beneath virtual keys
• if resized version show "sending resized image" otherwise "send" (as it is now)
• test with disabled data
  • show resized image if available
  • show thumbnail if resized image not available
  • show (something smart) if both is not available -> default image icon
• on air plane mode: snackbar is shown all the time as resized download files -> prior check of connection

Assumptions:

• users do not want to download the whole image, instead just like streaming have only a resized version
• if an user wants to have many images in original quality, he can synchronize the folder

This leads us to

• always show a resized version
• if an user zooms in (> 2x) a snackbar "download full image: yes" will be shown (on every time)
• (to have the old behaviour: add setting "click on image downloads full image" (as checkbox))

Update: Talked to Jan @conf:

• behvaviour setting can be removed
• otherwise approved

[tobiasKaminsky]

Closing in favor of #1710
Please do not yet delete the branch.