feat: added the ability to set the size of an icon when using a dot s…

[jamespcole]

This is a small change allowing the icon size to be scaled relative to the node when using the dot shape.

The existing "icon.size" property is ignored when using a "dot" shape so this new option is intended to enable specifying the icon size relative to the shape size.

To use this a "scale" setting can be added to the icon settings:

{
    shape: 'dot',
    size: 30,
    icon: {
        face: 'FontAwesome',
        color: '#2B7CE9',
        scale: 0.9,
    }
}

Thank you for contributing to vis.js!!

Please make sure to check the following requirements before creating a pull request:

• All pull requests must be to the develop branch. Pull requests to the master branch will be closed!
• Make sure your changes are based on the latest version of the develop branch. (Use e.g. git fetch && git rebase origin develop to update your feature branch).
• Provide an additional or update an example to demonstrate your changes or new features.
• Update the documentation if you introduced new behavior or changed existing behavior.
• Reference issue numbers of issues that your pull request addresses. (If you write something like fixes #1781 in your git commit message this issue gets closed automatically by merging your pull request).
• Expect review comments and change requests by reviewer.
• Delete this checklist from your pull request.

[exoego]

Code is LGTM.

It would increase a chance to get merged if new option is added to

• docs: https://github.com/almende/vis/blob/5563fc616885578ad51b2dfa6ccf70ccebf06126/docs/network/configure.html#L133
• examples: https://github.com/almende/vis/blob/master/examples/network/nodeStyles/icons.html

[mojoaxel]

@jamespcole Thanks! But I have some questions:

• There is already a icon.size option. Is this not enough?
• Every new option needs to be documented in the docs as well. somewhere near here
• If you still think this feature is needed could you please extend the icons example