Inventaire integration

[xplosionmind]

Is your feature request related to a problem? Please describe.
It would be great if a user could:

• directly import data from their own Inventaire account
• synchronise the the books added to Inventaire and vice-versa
• Linking the same individual’s Bookwyrm and Inventaire profiles so that, until the features in Books exchanges #1127 are implemented, a user could make use on Inventaire of the features missing on Bookwyrm.

Describe the solution you'd like
Doing all of the above via the GUI without having to download, tweak in order to maximize compatibility and then re-upload exported data.

Describe alternatives you've considered
Doing all of the above manually.

Additional context
none

[mouse-reeve]

Depending on how/if Inventaire implements ActivityPub, interoperability may also been an alternative path to syncing accounts (inventaire/inventaire#187)