[CORE3] - Line Items

1. Line Items' datamodel needs to be designed in wrt following:
2. Line Items need to have a quantity
3. Line items need to have an expected cost per item
4. Line items need a brief justification on item + unit cost of item
5. Line items need to be linked to a Reimbursement Request
6. Line items must exist within the context of a Purchase Request ONLY
7. Line items need to have actual quantity and actual cost per item which is only filled after the reimbursement request comes in
8. Line items need to have one of the following status "Line item | in reimbursement | archived"