Handle src/bin folders that are the same as project root folders

It is possible to create source and binary folders that are the same as
the project root folder. The easiest way to do this is to use the "Use
project folder as root folder for sources and class files" option in the
new Scala project wizard.

Scala IDE is unable so far to handle these folders because the Eclipse
API itself seems to be unable to handle these folders. The common
operation to retrieve an IFolder is

project.getFolder(path)

which throws an exception in case `path` is the same as the path of
`project`.

The problem is fixed by not calling `getFolder` inside of `ScalaProject`
but by reusing an existing reference to the `IContainer` that already
references the correct location on the filesystem.

Fixes #1002146
scaliform default preferences changed

scaliform.DoubleIndentClassDeclaration preference changed from "false" to "true" according to Scala Style Guide.
https://github.com/mdr/scalariform#doubleindentclassdeclaration

Fixes #1002321
Merge pull request #858 from sschaef/t1002146-handle-root-source-folders

Handle src/bin folders that are the same as project root folders
Merge pull request #860 from caiiiycuk/scala-ide-style-1002321

scaliform default preferences changed
Wraps the Java spelling API call

As it will return 'null', if there are no spelling mistake to fix.
Avoid logging twice the same stack trace

SafeRunner already log the stack trace. Tweaked the error message to point
to this stack trace.
Merge pull request #863 from skyluc/issue/class-cast-exception-2317

Quick fix exceptions