DRY Gemfile and database.yml
Merge pull request #32 from vexor/refactoring

DRY Gemfile and database.yml
Add current company scope to SSE

* using UUID for pk in companies
* migrate exsiting tables to company_id:uuid
* simplify SSE messages
* add scope to SEE messages: current company
* fixed factories for company_id_fkey, implicitly create company
* create FK for projects -> builds -> jobs -> job_logs
* restore unique indexes after company uuid migration
Merge pull request #33 from vexor/uuid_primary_keys

Add current company scope to SSE
Can destroy users

* add destroy action to /api/users, check does user have any companies
* add Delete link to user table
Company usage statistics

* add CompanyUsage class and api action /api/companies/usage
* add usage page
* add billing_started_at to company, add Invoice model
* add back_office column to user