Upgrade to CTD 9.7. Include SLF4J log service.

[fvgh]

Upgrade to CDT 9.7.
Replaced Spotless CDT specific log service by the common SLF4J log service provided by spotless-eclipse-base.

[fvgh]

@nedtwigg The release date in the CHANGES.md still contains a todo.
As described in #232, I checked the IncludeOrganizer. I actually had a prototype working. But seeing the dependencies on internal interfaces and the quite limited result, it was not worth the effort.
Hence I see currently no need for further changes on this spotless-eclipse-cdt.
Feel free to publish on Maven Central whenever you find time.

[nedtwigg]

Seems that p2 repository was needed. I removed it, and I'm getting this error:

Could not resolve all files for configuration ':embeddedJars'.
> Could not find any matches for p2:org.eclipse.core.variables:+ as no versions of p2:org.eclipse.core.variables are available.
  Searched in the following locations:
      https://repo.maven.apache.org/maven2/p2/org.eclipse.core.variables/maven-metadata.xml
      https://repo.maven.apache.org/maven2/p2/org.eclipse.core.variables/
      https://jcenter.bintray.com/p2/org.eclipse.core.variables/maven-metadata.xml
      https://jcenter.bintray.com/p2/org.eclipse.core.variables/
      file:/Users/ntwigg/.m2/repository/p2/org.eclipse.core.variables/maven-metadata.xml
      file:/Users/ntwigg/.m2/repository/p2/org.eclipse.core.variables/
      file:/Users/ntwigg/Documents/dev/spotless/_ext/eclipse-cdt/build/p2asmaven/maven/p2/org.eclipse.core.variables/maven-metadata.xml
      file:/Users/ntwigg/Documents/dev/spotless/_ext/eclipse-cdt/build/p2asmaven/maven/p2/org.eclipse.core.variables/
  Required by:
      project :

I have some guesses for a fix, but I'll leave it for you @fvgh in case I'm missing some important context.

[fvgh]

Sorry should have not committed in a hurry...

[nedtwigg]

No worries, that's would code-review is for :) 9.7.0 published just now.