Bounds checking: check both lower and upper bounds during node collision resolution

[jayaddison]

During development of #71, I encountered situations where the resolveCollisionsBottomToTop was being called with out-of-bounds values for the function argument i.

For consistency and safety, this change adds upper and lower bounds checks to both resolveCollisionsBottomToTop and resolveCollisionsTopToBottom.

The JSON data in use was:

{
    "nodes": [
        { "name": "Person 1", "type": "person" },
        { "name": "Person 2", "type": "person" },
        { "name": "Person 3", "type": "person" },
        { "name": "Person 4", "type": "person" },
        { "name": "Person 5", "type": "person" },
        { "name": "Project 1", "type": "project" },
        { "name": "Project 2", "type": "project" },
        { "name": "Project 3", "type": "project" },
        { "name": "Project 4", "type": "project" },
        { "name": "Project 5", "type": "project" },
        { "name": "Project 6", "type": "project" },
        { "name": "Project 7", "type": "project" },
        { "name": "Deliverable", "type": "deliverable" }
    ],
    "links": [
        {
            "source": "Person 1",
            "target": "Project 1",
            "value": 3
        },
        {
            "source": "Person 2",
            "target": "Project 2",
            "value": 1
        },
        {
            "source": "Person 3",
            "target": "Project 3",
            "value": 1
        },
        {
            "source": "Person 4",
            "target": "Project 4",
            "value": 1
        },
        {
            "source": "Person 1",
            "target": "Project 4",
            "value": 1
        },
        {
            "source": "Person 1",
            "target": "Project 3",
            "value": 1
        },
        {
            "source": "Person 1",
            "target": "Project 2",
            "value": 1
        },
        {
            "source": "Person 5",
            "target": "Project 3",
            "value": 1
        },
        {
            "source": "Person 3",
            "target": "Project 5",
            "value": 1
        },
        {
            "source": "Person 4",
            "target": "Project 6",
            "value": 1
        },
        {
            "source": "Person 2",
            "target": "Project 7",
            "value": 1
        },
        {
            "source": "Project 3",
            "target": "Deliverable",
            "value": 1
        },
        {
            "source": "Project 4",
            "target": "Deliverable",
            "value": 1
        }
    ]
}

Revives #80.

[jayaddison]

Closing some old/stale pull requests.