This commit adds support for unfurling static image URLs (not GIFs, not animated WebPs), such as https://placehold.co/600x400@2x.png. It also compresses images before returning them as data URIs to clients.
About compression: the compression strategy leverages the existing function images.CompressToFileLimits. A more comprehensive logic to consider the possibility of multiple image URLs being unfurled simultaneously is yet to be implemented.
Closes#3761
Some functions split to be more cohesive, custom PostSteps are
stored as pointers to allow their retrieval and parameters passing
in runtime if needed (some extra work is dropped and TBD
when needed)
The only place where appDB is used in wallet is activity,
which refers to `keycards_accounts` table. So a temporary
table `keycards_accounts` is created in wallet db and updated
before each activity query.
Ivan Belyakov
Andrea Maria Piana
Icaro Motta
