Display input and output types in outline, load commands only once
Generate DOT with Xtend to visualize Flux workflows with Zest

On saving a *.flux file in the editor, the generator will create a
corresponding *.dot file in the project's `src-gen` folder.

With the Zest graph view open and listening to changes in the
workspace (see user guide for usage details), this visualizes the
workflow currently edited in the Flux editor (see also #7).
Fix issues with the Xtend generator in a clean build

- Add dependency to `org.eclipse.xtend.lib`
- Generate Xtext artifacts before compiling Xtend generator
- Remove `src-gen` on `mvn clean`
- Fix formatting of pom.xml
Merge pull request #24 from fsteeg/outline

More visual clues for editing Flux files