SVGHMI: add warning_labels, same as optional_labels but emits warnings at build time if element is missing.

SVGHMI: update generated XSLT files

SVGHMI: generalize detach/re-attach of binary choices for ToggleButton, PushButton, Button and Keypad's Shit and CapsLock.

SVGHMI: also use order-preserving detach re-attach for hiding and showing active and inactive state.

SVGHMI: fix Switch widget so that order of choices elements is preserved across detaching and re-attaching.

SVGHMI: update generated xslt files

SVGHMI: nasty scope shadowing bug... was making funny recursion, leading to really slow interaction.

SVGHMI: fading page switch : to avoid blinking, page stays black once fading finished and next page is still not ready.

SVGHMI: fading page switch : defer update of classList to next animate() call when finishing transition.

classList update was happening in the same call as switch_page(), but this call is not meant to do any change in the DOM. This was triggering unwanted style and layout recomputation.

SVGHMI: rework Switch widget : detach/attach elements instead of hiding with style.display, detach all possible choices at init.

SVGHMI: add fading transition to make page switch feel more responsive on slow machines.

SVGHMI: add a way for widgets and other yslt2 files to add css definitions to resultng page.

SVGHMI: update generated XSLT filesw

SVGHMI: XY graph build produces error message if provided curve_N are not consistent.

SVHMI: Keyboard: Replace untouched value when typing directly after open. Make info string (HMI variable name) optional.

merged