Sanitize URIs for when dropped from external browser

While going through the latest enRoute tutorials on Linux I noticed that when using the external browser (setup through preferences) and I drag-n-drop the vignette onto the local jpm repository, it fails to parse the URL and load the dependency.  I traced through both bndtools and bnd code and found that the URL that is coming in has invalid characters for a URI object, namely it has a "\n" in the string that is copied from the system clipboard like this:

```
https://www.jpm4j.org/#!/p/sha/C621B54583719AC0310404463D6D99DB27E1052C//0.0.0\n1.3.1
```

When the conversion from String to URI happens it will fail with a URI exception.  So in the Converter class here as well as one place in bndtools I needed to add some code to sanitize the string before trying to allow the URI conversion to take place.  
In https://github.com/bndtools/bndtools/pull/981 you hane > -1. Should be consistent.