Backport PR #7192 on branch 1.1.x (progress on icons: added inline svg icon support to toolbar buttons)

[meeseeksmachine]

Backport PR #7192: progress on icons: added inline svg icon support to toolbar buttons

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[jasongrout]

Let's discuss this (and backwards compatibility in general) in the dev meeting tomorrow before merging. If we merge, I'll make a release tomorrow with it to fix a number of issues that have come up.

[telamonian]

Waaait... now I'm extra confused. The changes in #7192 made it into the 1.1.4 release, right? But this backport didn't get merged? How did that happen?

Relevant quote from @jasongrout on Gitter:

we have a 1.1.x branch and a 1.x branch. Both need the backport. As a matter of process, it's good to only backport to 1.1.x from 1.x since then you know that patches in 1.1.x are also in 1.x.

[jasongrout]

Huh. That is confusing. Here is the backport that was merged: #7236

Not sure why I didn't use this PR. I do remember there being some merge conflicts with a backport of #7192.

Anyway, closing since a backport was merged.