Allow creating and modifying allocations

[QuanMPhm]

Closes #47. After digging around DRF's documentation on serialization, it turned out the code changes would be a bit more complicated than I expected. I will submit a draft for now to demonstrate my current direction.

My draft allows creating new allocations through api/allocations by posting a json payload like this:

{
    'allocationattribute_set': [
        {'allocation_attribute_type': 'OpenShift Limit on CPU Quota',
        'value': '4'},
        {'allocation_attribute_type': 'OpenShift Limit on RAM Quota (MiB)',
        'value': '4096'},
    ],
    'project_id': 3,
    'resources_id': [1]
}

The output from the allocations API has been changed slightly. It now outputs this:

{
    "id": 31025,
    "project": {
        "id": 3,
        "title": "NERC-TESTING-1",
        "pi": "[[email protected]](mailto:[email protected])",
        "description": "khkjhkl\r\njjhhjk",
        "field_of_science": "Polar Ocean and Climate Systems",
        "status": "New"
    },
    "description": "",
    "resource": {
        "name": "microshift",
        "resource_type": "OpenShift"
    },
    "status": 1,
    "allocationattribute_set": [
        {
            "allocation_attribute_type": "Allocated Project Name",
            "value": "nerc-testing-1-dc43c5"
        },
        {
            "allocation_attribute_type": "Allocated Project ID",
            "value": "nerc-testing-1-dc43c5"
        },
        ....
    ]
}

I will implement the "update" feature once given the green light on this approach.