Replace SQLite with PostgreSQL (WIP, DO NOT MERGE!)

Submitting what I have so far in terms of migrating to PostgreSQL, in case others want to collaborate. It's failing `rake db:migrate` with the following error now:

```
==  BarclampImportCrowbar: migrating ==========================================
rake aborted!
An error has occurred, this and all later migrations canceled:
PG::Error: ERROR:  current transaction is aborted, commands ignored until end of transaction block
:             SELECT a.attname, format_type(a.atttypid, a.atttypmod),
                     pg_get_expr(d.adbin, d.adrelid), a.attnotnull, a.atttypid, a.atttypmod
              FROM pg_attribute a LEFT JOIN pg_attrdef d
                ON a.attrelid = d.adrelid AND a.attnum = d.adnum
             WHERE a.attrelid = '"snapshots"'::regclass
               AND a.attnum > 0 AND NOT a.attisdropped
             ORDER BY a.attnum
...
/tmp/crowbar-dev-test/opt/dell/crowbar_framework/app/models/barclamp.rb:450:in `create_template'
/tmp/crowbar-dev-test/opt/dell/crowbar_framework/app/models/barclamp.rb:438:in `block in import'
/tmp/crowbar-dev-test/opt/dell/crowbar_framework/app/models/barclamp.rb:361:in `import'
/tmp/crowbar-dev-test/opt/dell/crowbar_framework/app/models/barclamp.rb:348:in `import_1x'
/tmp/crowbar-dev-test/opt/dell/crowbar_framework/db/migrate/20120731230001_barclamp_import_crowbar.rb:18:in `up'
...
```