Expose sizing and position properties from iron-image (update)

[matthewpull]

Fixes #60

PR #62 also fixes this issue, but is a year old. This PR is an attempt to gain traction on fixing the issue and includes the two test cases required.

This is my first PR :tada:, so if I have made a rookie mistake or missed anything please let me know and I'll fix my error.

Cheers!

[notwaldorf]

Omg, finally looking at this. Sorry about that! @bicknellr for a double check, but this looks okay to me.

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[Pupix]

Is this going to get merged anytime soon?