Enhance Eclipse usage instructions

Updates to instructions for setting up DbFit in Eclipse.
> Yes, we could just say execute ./gradlew eclipse from the top level dbfit directory.
> 
> I don't know about for IDEA though - does that need to be run from dbfit-java?
> 
> I think there's no issue with the commands for each being run from different dirs.

I think for IDEA It's the same as Eclipse and looking at its description. It's docs actually assumes `gradew` script in the current dir `./gradlew idea`.


> I do need to update the doc to say to also ignore the FitNesseRoot project that's hanging around from the old SVN repo unless we should delete this now?

As far as I see - `.project` files should be ignored as per `.gitignore` so following both are candidates for removal:
```
FitNesseRoot/.project
dbfit-java/oracle/.project
```