major refactor to wrap retieval of macros all around ISymbianBuildContext, to avoid need to access internal apis. Added getTargetTypeMacro(String targettype),
List<IDefine> getMetadataMacros(), List<IDefine> getBuildMacros().
<contexts>
<context id="hoverHelpContext">
<description>Hover Help Guide</description>
<topic href="resources/help context/dl_hover/html/getting_started.html" label="Overview"/>
<topic href="resources/help context/dl_hover/html/setup.html" label="Set Up"/>
<topic href="resources/help context/dl_hover/html/preferences.html" label="Preferences"/>
</context>
</contexts>