Two-stage ("soft") delete user experience

[devinreams]

Needs UX to decide what we want to build.

Then to implement in datastore: https://github.com/mozilla-lockbox/lockbox-datastore/issues/16

And then implement the user experience here, obviously.

[changecourse]

Entry Details (with Delete btn) : https://mozilla.invisionapp.com/share/MHEBCD4PK#/262163357_1-1-1_Lockbox_Home_-_View_Entry

Home Screen (after deletion, displays notification with 'UNDO') : https://mozilla.invisionapp.com/share/MHEBCD4PK#/262163358_1-1-3_Lockbox_Home_-_Entry_Deleted

[linuxwolf]

@changecourse a couple of questions:

• At what point can delete not be undone?
• Is the concept of "remove then purge" (e.g. "trash bin") something that might be foreseeablely surfaced?

There are a few approaches that can be taken architecturally, but it would help to understand how long "stale" data can remain.