Handle the XLIFF tool element using properties and annotations on a
StartSubDocument and AltTrans Annotation.

Conflicts:
	okapi/filters/xliff/src/main/java/net/sf/okapi/filters/xliff/XLIFFSkeletonWriter.java
Handle the XLIFF phase element using properties and annotations on a StartSubDocument
Add XLIFF state-qualifier as TU target property
Remove whitespace when removing ITS elements in the skeleton