multiple instances of passman may become desynchronized

[IsaacSteadman]

Change passman to pull from the server and check the last modified date and compare it to the last modified date of the data the current instance pulled from the server and perform a merge if necessary

merge may require user interaction to decide which changes from which password vault to keep

[IsaacSteadman]

Or when saving add a “if-modified-last” or related header on the PUT request

[IsaacSteadman]

partial duplicate of issue #12

this issue scope is changed to allow the user to respond to a 409 conflict (If-Unmodified-Since) by merging in some sort of diff editor.