Exclude some DEBUG logging from Blitz.log

The import logs require some classes to log at DEBUG, those same classes should not log at this level in the blitz log. This PR uses an EvaluatorFilter to exclude some DEBUG logging from the blitz log. Without this PR both of the two sections below would be similar to the first.

Section of import log:
```
2013-12-12 17:18:52,752 DEBUG [    o.s.blitz.repo.ManagedImportRequestI] (3-thread-3) Image Count: 69
2013-12-12 17:18:52,752 INFO  [    o.s.blitz.repo.ManagedImportRequestI] (3-thread-3) File format: Deltavision
2013-12-12 17:18:52,752 INFO  [    o.s.blitz.repo.ManagedImportRequestI] (3-thread-3) Base reader: loci.formats.in.DeltavisionReader
2013-12-12 17:18:52,753 DEBUG [    o.s.blitz.repo.ManagedImportRequestI] (3-thread-3) Step 0
```

The equivalent section from the blitz log:
```
2013-12-12 17:18:52,752 INFO  [    o.s.blitz.repo.ManagedImportRequestI] (3-thread-3) File format: Deltavision
2013-12-12 17:18:52,752 INFO  [    o.s.blitz.repo.ManagedImportRequestI] (3-thread-3) Base reader: loci.formats.in.DeltavisionReader
```
This filter has the side-effect of excluding all `omero.*` at DEBUG level from the blitz log regardless of the setting of
```
  <logger name="omero" level="INFO"/>
```
Thus the only effective way of raising this to DEBUG would be to disable or modify the relevant filter. It may be that the logging of `omero.*` can be refined at a less granular level.

There may also be a neater way of doing this but see: http://jira.qos.ch/browse/LOGBACK-625

--no-rebase