SVGHMI: allow i18n of formated strings of HMI:Messages. This was by construction impossible since formating was given as an argument. Now added optional "format" labelled element in HMI:Display, so that it can be translated, when labelled "_format".
<xsd:attribute name="Compiler" type="xsd:string" use="optional" default="gcc"/>
<xsd:attribute name="CFLAGS" type="xsd:string" use="optional" default=""/>
<xsd:attribute name="Linker" type="xsd:string" use="optional" default="gcc"/>
<xsd:attribute name="LDFLAGS" type="xsd:string" use="optional" default=""/>