Set file encoding to `UTF-8` for tests execution in Tycho

* Had to change the return type of the Snowman to `AnyRef` for
  the test to pass against both Scala 2.9 and Scala 2.10 (the
  returned name for the `String` type is different in 2.9 and
  2.10)

* Pass `-Dfile.encoding=UTF-8` to Tycho test task.
* Re-enabled encoding test.

Fix #120
Merge pull request #130 from dotta/issue/pass-encoding-to-tycho-test-task-124

Set file encoding to `UTF-8` for tests execution in Tycho
Allow users to specify VM arguments

Added preference for specifying VM arguments to be used by worksheet processes.
Adjusted preference page layout to accomodate for new field
Error dialog reports last output upon abnormal worksheet termination

Fix #125
Removed string interpolation Re #125
Switched over to DisplayThread.asyncExec Re #125
Merge pull request #131 from nadavwr/vmargs-#125

Allow users to specify VM arguments
Renames LexicalStructure to LexStructure

The old name was creating ambiguous error with global._
Merge pull request #133 from skyluc/issue/2.11.0-M3-compatibility

Renames LexicalStructure to LexStructure
Fixed typo in README
Unified handling of VM arguments and document's encoding

Commit SHA: 342e4bc8533495f1a1a7f8c5ee60925516a52558 allowed users to
pass specific VM arguments to the VM created to execute the worksheet.
However, that commit caused the worksheet file's encoding to be defaulted
to the system's encoding, if the "-Dfile.encoding" vm argument was not
explicitly provided by the user.

That's annoying, as the default encoding should just be the project's
encoding. And that's exactly the behavior implemented in this commit.

This commit also introduces a `VmArguments` class, which is a simple
container for manipulating VM arguments. For sure it could be much more
richer than it is now, but that is out of the scope of this commit.

Fix #138
Merge pull request #139 from dotta/issue/file-encoding-138

Unified handling of VM arguments and document's encoding