Removed unique constraint on account name

Per https://assemblymade.com/support-foo/wips/63 a slug is being added
which is the identifier for the account.  It'll be URL-safe and unique
across the app.

Therefore I propose the "name" attribute is repurposed simply as the
"display name" of the account.  It therefore should not be unique.
Added a user to the seeds file
Add account slugs

Per https://assemblymade.com/support-foo/wips/63
Merge pull request #14 from drewblas/add_account_slug

Add account slug
Making conversations archivable

Conversation model are now able to be archived with
```@conversation.archive``` should be called on _send & archive_ call.

Conversations can be unarchived with ```@conversation.unarchive```
should be called on incoming email or when a user "opens" a
conversation.
Moving to an more generic status column instead

To get unarchived conversations now user ```Conversation.unarchived```
instead
Making some smart moves on status column for Conversations

Removing ```unarchive``` method for time being.
resolving conflict in schema
Add mailman gem
Set conversation number to auto inc within account_id scope
Set Mail.delivery_method to :test in the test env.
Add entry point for new email in Messages::Email.receive
Add bin/mailman script to fetch email via IMAP
Update README.md with mailman info
Add Sequential gem to handle conversation number
Fix tests