"Created" date

[kirillt]

It seems that we have 3 different ways to provide created_at timestamp:

• extracted automatically for specific resource kinds, e.g. from EXIF must be stored in .ark/cache/metadata
  • ARK-Builders/ark-components#56
• specified manually by user or automatically by an app must be stored in .ark/user/properties
  • ARK-Builders/arklib-android#89
• generated automatically for any resource during its first indexing must extend .ark/index
  • https://github.com/ARK-Builders/arklib/issues/66

[kirillt]

This created_date attribute must be possible to use in resource sortings.