Support to load different image variant variants in hst:html depending on CONTEXT

Developers can then depending on the context show small or large image : Thus, small image for mobile, medium for ipad, large for site
Secondly, think about device detection: When low bandwidth detected, show low resolution, otherwise high

I will do for this the following :

1)

Add a new hst-core.tld tag : <hst:imagevariant>

This tag gets some parameters like:

1) Which variant to use (for example myhipporpoject:thumbnail)
2) Which variant to replace (for example myhippoproject:original ). If this property is missing, (1) is used for all variants
3) fallback = true | false : If the variant to use does not exist, default back to the original one if true. Default fallback will be false

This imagevariant element can only be placed within the hst:html tag as child tag

2) Next to the ContentRewriter interface, I'll add the ImageVariantRewriter interface that at least contains:

void setImageVariant(some image variant obj representing <hst:imagevariant> parameters)

3) SimpleContentRewriter will also implement ImageVariantRewriter :

Note that because I want to backport this feature, I do not want to add the setImageVariant method to the ContentRewriter API because custom projects might have implemented it themselves. Unless we assume they all extend the AbstractContentRewriter... I think that was the purpose of AbstractContentRewriter. If so, I could add the setImageVariant method to ContentRewriter and implement it in AbstractContentRewriter. That might be better...

WDOT?

Regards Ard