URL's for sharing records

[JeffAbrahamson]

Add two flags:

--export-as-url produces an srd://d/ url, the tail of which (after the "d/") is an appropriately escaped representation of an srd record. Prompts for two passwords: the db password (to read the record) and a URL password (to decrypt the URL). Also takes matching flags to narrow selection of records.

--import-url takes a URL on the commandline. Requests two passwords, the local db password and the URL password. If any record exists in the current db, options to edit, auto-merge (probably means concatenate), or cancel. If the URL represents multiple records, the action should be atomic and not take effect until after all user interaction.