Bug 561415 - Make source tab in pom editor pluggable/replaceable

Move the WTP-based Maven text page and all the code that depends on
wtp.ui to org.eclipse.m2e.editor.xml bundle; then contributes the editor
to existing
pageFactories extension point.
PageFactories extension that provides a source editor just have to call
MavenPomEditor.setSourcePage(...) to register themselves as the source
page. The generic editor is used as fallback if no page registers itself
as source editor.

Use GenericEditor as fallback editor if MavenStructuredEditor couldn't
be loaded via extension point

Change-Id: Iea35471913cd0bea02133982dc1011bef39088f7
Signed-off-by: Andrew Obuchowicz <aobuchow@redhat.com>
55 files changed