Accept a share of private files

[icidasset]

Adds a UI that allows people to accept a share.

Then updates your filesystem and data root, after which it gives you the following:

More info about sharing private files:

• https://github.com/fission-suite/webnative/pull/331
• https://talk.fission.codes/t/initial-private-sharing-implementation/2140
• https://whitepaper.fission.codes/file-system/shared