1.2.3.) Account model   [belongs_to :customer, has_many :offers, through: services]
      - customer_id         [references/int]
      - saldo               [decimal - 9,2]
      - status              [string] [active / blocked]
      - block_reason        [string]
      - db_name
      - db_user
      - db_password

    1.2.4.) Service model   [belongs_to :offer]
      - service_name                [string] [sale / crm / schedule]
      - offer_id            [references/int]

    1.2.5.) Offer model     [has_many :services]
      - name                [string]
      - service_name        [string] [sale / crm / schedule]
      - limits              [hstore]

Example scenario:
 - table offers
    id: 1, name: "Winter offer for crm", service_name: "crm", limits: {contacts_limit: 5}
    id: 2, name: "Winter offer for sale", service_name: "sales", limits: {sales_limit: 100}

 - table services:
     id: 1, service_name: "crm", offer_id: 1
     id: 2, service_name: "sales", offer_id: 2

 - table account_services:
    id: 1, account_id: 1, service_id: 1
    id: 2, account_id: 1, service_id: 2