Added default background color to WebEditorMapper

WebEditorMapper is using "background" theme color as the default
background instead of null.
Added pluginKey="declBoder"
Added 7 mappings

Markdown (winterwell.markdown)
Console (org.eclipse.debug.ui)
CVS (org.eclipse.team.cvs.ui)
Spket JavaScript (com.spket.js)
Spket XML (com.spket.xml)
XSL (org.eclipse.wst.xsl.ui)
DTD (org.eclipse.wst.dtd.ui)