Rename `findWord` to `getWord`

The rename is necessary because methods starting with `find` should
return an `Option` and later refactorings are built upon this change.
Reformatting in `ScalaWordFinder`
Fix AIOOBE in ScalaWordFinder

The exception could occur because an arbitrary Seq can be passed to the
method findWord and not just some special wrappers that are defined in
the overloaded alternatives. Because there were also no offset checks,
the result would have been completely useless if this method would have
succeeded without an exception.

Therefore, this commit introduces offset checks and returns None if the
offset is invalid. In order to return an Option, the API of findWord
had to change. Because the word finder is used in some AspectJ code, a
new method `getWord` was introduced in a former commit, which returns
null instead of a `None`.

Another change is that findWord doesn't accept a Seq anymore, but an
IndexedSeq. Otherwise a passed linked list would result in an
inefficient implementation.

Fixes #1002238
Rename constructor parameter in ScalaPresentationCompiler

One constructor parameter in ScalaPresentationCompiler had to change
its name because it would hide the super implementation otherwise,
which can easily lead to a bug.
roll back on making the output of ScalaWordFinder an Option
Merge pull request #813 from huitseeker/792-reissue

Fix ScalaWordFinder AIOOBE