Eclipse command for finding occurrence of selection

This commit provides an Eclipse command for finding all
occurrences of the Scala entity that is selected in the
current editor.

It adds a new context menu to the Scala editor.

Currently just supports methods

Fixes #1001686 #1001664
Merge pull request #36 from mads379/1001686-integrate-with-eclipse

Eclipse command for finding occurrence of selection
Can now find occurrences of apply

The Finder could previously not find these occurrences as
the don't appear Apply(Select(apply),...) but rather
Apply(Ident(Foo),..).

I fixed it by making it possible to search for multiple
words when looking for occurrences (this will also be needed
later when searching for aliases). When searching for an apply
invocation i will now search for explicit invocations (i.e. apply)
and implicit invocations (i.e. Foo). So it will search for apply and
the name of the owner of the apply method.

Fixes #1001736
Merge pull request #37 from mads379/1001736-apply

Can now find occurrences of apply
Added mockito jar in classpath of test project
Refactoring - Finder no longer extends Index

Composition here seems to be better than inheritance. A `Finder` is not an
`Indexer`.
Refactoring - Finder no longer extends ProjectFinder

Composition here seems to be better than inheritance.
Refactoring - SourceIndexer no longer extends Index

Composition here seems to be better than inheritance. A `SourceIndexer`
is not an `Index`. Rather, a `SourceIndexer` uses an `Index`, which is
why composition is better in this case.