Merge pull request #366 from greezybacon/feature/i18n-initial-data

Add language selection to installer

Reviewed-By: Peter Rotich <peter@osticket.com>
Merge pull request #367 from greezybacon/issue/plugins-revisited

Revisit plugin manager

Reviewed-By: Peter Rotich <peter@osticket.com>
First stab at pluggable attachment storage
Retire attachment chunk orphan cleanup
Add better error handling for file storage backends
Migrate file metadata table

  * Include a `bk` column to store the storage backend
  * Include a `signature` column which represents a repeatable hash of the
    file contents
  * Rename `hash` to `key` since it isn't a real hash
Fix several issues from initial mockup