[BasicUI] Use inline SVG for "colorless" SVG icons

[lolodomo]

Related to #1743

Use a HTML svg element (inline SVG) instead of a img element
when the icon servlet returns a SVG icon containing "currentColor".

Then it is possible to adjust the color of these icons by using the
iconcolor sitemapo attribute.

Signed-off-by: Laurent Garnier lg.hc@free.fr

[lolodomo]

This PR is currently based on PR #1792. I will rebase it when #1792 is merged. Edit: done.

The change is working well but I have still to check if cache is really working when using "fectch". It looks like it is not with Firefox.

The disadvantages of this change is that:

1. an icon is now potentially retrieved twice when a new page is opened
2. the weight of the page when using inline SVG is bigger than when using img tags
3. The browser cache when getting a new SVG icon may be not working (to be confirmed)

The big advantage is that you can now change the color of your icons (for colorless SVG icons).

This change will add nothing really new when using the classic iconset as all (or almost all ?) icons have hardcoded colors.

I could also make this new feature an option of Basic UI.

[kaikreuzer]

@lolodomo You asked for this to be reviewed, but the PR is still in DRAFT mode. Is this by accident?

[kaikreuzer]

This looks like some voodoo, but I trust you have tested it. 😄
Just one small comment below.

[lolodomo]

@lolodomo You asked for this to be reviewed, but the PR is still in DRAFT mode. Is this by accident?

My wish is to merge it before new milestone.
But I will add an option to let the user choose if he wants this feature or not. I will finish the PR probably Friday.

[lolodomo]

@kaikreuzer : PR is now fully ready for a merge.

With this sitemap:

	Frame label="Text icon color" {
		Default item=TestNumber icon="mic" iconcolor=[==56="blue", "yellow"]
		Default item=SetpointTemp icon="temperature" iconcolor=["yellow"]
	}

and the mic.svg being a custom icon containing currentColor as the fill color.

With the feature enabled: => inline SVG and color considered

With the feature disabled: => IMG and color ignored

[kaikreuzer]

Thanks!