SVGHMI: Meter widget accepts 2 arguments : min and max, taken in account when min or max text element is missing

SVGHMI: More precise error message on missing HMI path. Meter widget now defaults 0-100 range when min and max elements arent's present, without error.

SVGHMI: more whitespace fixes

SVGHMI: unlink clones (i.e. deep copy elements refered by svg:use) inside widget.

Designer can use Inkscape clones to duplicate similar assets accross widget. Those clones are unliked so that elements can be independently transformed by individual widgets.

SVGHMI: whitespaces and comments

SVGHMI: completely fixed indentation of generated widget description. Lets try to keep it as-is until we can use yslt indentation.

SVGHMI: re-indent generated JS

SVGHMI: detach/re-attach elements required by pages on page switch

This is meant to optimize performances with large drawings leading to long restyle or reflow.

SVGHMI: re-indenting

SVGHMI: declares pages detachable requirements as an object, to find more efficiently common requirements

SVGHMI: fix some JS + add generation of detachable elements, to be continued

SVGHMI: now compute discardable elements first so that we can do better grouping of required elements when sumarizing.

SVGHMI : documentation for new geometry intersection computation code + little fixes...

SVGHMI: detachable and discardable elements sets, Reworked geometric intersection, toward more accurate page content detection.

Moved page's widget/element dependency crawling functions so that it is possible to compute a global detachable and discardable elements sets.
Reworked geometric intersection detection logic to distinguish ovelapping and inclusion.
Goal is to include englobing and overlapping graphical elements, but not groups (would then include everything around...). Intermediate commit, to be continued.

SVGHMI : still trying to optimize. Added xslt code to identitfy minimum set of elements needed by a particular page. Plan is to remove unseen/unused elements from the DOM, and re-appending them later when used, on page switch. Disabled previous optimization.

SVGHMI: attempt to optimize for webkit, because of really slow style recompute in svg:use : "unlink clones" (as in inkscape) but stop deep-copy when meeting a widget, and create a new clone instead.