Don’t add an empty parameter list for Java getters.

Fixed #1002171
Use the computed (local) type in the completion proposal.

This offers more precise tooltip info for inferred types
at the point of application. For example:

```
val xs: List[Int]

xs.map(| // this will now show f: Int => B
```
Merge pull request #786 from dragos/issue/completion-java-getters

A couple of simple improvements in completions
Set ScalaImages constants as API

The internal method helpers are moved in OSGiUtils