ImageJ startup is too fragile

From a fresh Fiji installation, try this:

``` shell
$ rm jars/bio-formats/*.jar
$ Contents/MacOS/ImageJ-macosx
```

And the application will fail to start up with an error similar to:

```
java.lang.IllegalArgumentException: Invalid service: io.scif.ome.services.DefaultOMEMetadataService
at org.scijava.service.ServiceHelper.createExactService(ServiceHelper.java:280)
*snip*
Caused by: java.lang.ClassNotFoundException: loci.common.services.ServiceException
at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
```

We specifically tried to address this sort of fragility by adding a `scijava.context.strict` system property, which tries much harder to continue creating the context despite such issues, but adding `-Dscijava.context.strict=false` to the above program launch does not alleviate the issue.

Investigation needed into how to improve the situation.

Reproduce the failure from a fresh Fiji installation by removing jars/bio-formats/*.jar and launching Contents/MacOS/ImageJ-macosx, then compare it with scijava.context.strict=false. Start from the ServiceHelper.createExactService stack trace and the DefaultOMEMetadataService/ClassNotFoundException details. Done means the startup fragility is addressed and the missing-jar scenario is verified.

Written by the indexing model from the issue text.