Proposal: add icons to the XWiki Icon Set

[surli]

@CharpentierLucas

@vmassol

• The icon for move seems weird for silk as it’s a left arrow.

• The icon for resize-horizontal seems weird for silk as I don’t see what’s horizontal in the chosen icon

Unfortunately, silk was created in 2005 and not updated for a long time, so there’s some huge holes in its icon theme cover. When checking out a list of the icons in silk, I could not find anything closer to those we would expect for those actions.
I think it’s more important to have an icon set that can represent a variety of icons, even if silk is a bit left behind. If we don’t provide enough icons in the set, devs will need to:

• hard code icons, defeats the purpose of having an icon set (see Loading…).
• use icons that are not appropriate to the context. E.g. using a burger menu icon instead of a move icon

Regarding silk shouldn’t we just start deprecating it? As you said it’s starting to get old, and I think we’re all more relying on FA those days than on silk. IMO it would make sense to deprecate it and stop bundling it in the future, maybe when we move to 16.x or 17.x.