Support for drop to frame

Note that it can skip some frames as StepInto does this intentionally
New File Wizard works with projects whose source dir is the root dir

It is not possible to create an instance of `IFolder` from a project path.
However, this behavior is required to create a file in a source dir that
is the same as a project dir. Therefore we switched from `IFolder` to
`IContainer` in the traits `NewFileWizard` and `FileCreator`.

Fixes #1002332
Merge pull request #871 from sschaef/t1002332-wizard-root-source-folders

New File Wizard works with projects whose source dir is the root dir
Merge pull request #859 from mpociecha/feature/drop-to-frame

Support for drop to frame
Bump development version to 4.1.0
Merge pull request #872 from dragos/issue/bump-version

Bump development version to 4.1.0
Fixes race condition during hyperlinking

Calling `Symbol.toString` outside of the Presentation Compiler Thread  can
result in a race condition, as demonstrated by the stacktrace in the ticket.

Fix #1002352
Merge pull request #873 from dotta/issue/race-condition-hyperlinking-1002352

Fixes race condition during hyperlinking
Partial revert of d9fbd270

Reverted the logic change, and updated the tests to correctly fail.
AssertionError exception should not be rethrown, has they can occur during
normal presentation compiler operation.

Fixes #1002355
Create the right ElementInfo for package declaration.

This resulted in a ClassCastException before.

Fixed #1000572.
Merge pull request #876 from skyluc/issue/AssertionErrors-1002355

Partial revert of d9fbd270
Correctly handle NullaryMethodTypes in the java type mapper

Fixed #1001734. No test since I cannot reproduce this reliably.
Merge pull request #878 from dragos/issue/package-decl-class-cast

Create the right ElementInfo for package declaration.
Merge pull request #879 from dragos/issue/assertion-error-fields

Correctly handle NullaryMethodTypes in the java type mapper