Allow creation of multiple root goals and removal of a root goal in the impact model

[Berk Duran]

An Impact Model can have more than one root goal in the same layout and it should allow the designer to convert a root goal into an intermediate goal via adding a contribution from it to another.

When the root goal of an Impact Model layout changes, that layout should now be associated with the new root.

[Berk Duran]

References #492

Removes the error popup when a contribution is created from a root goal.

→ <<cset e2605be36086>>

[Berk Duran]

References #492

When a contribution is added from the root goal on the layout, makes the new root the new key of that layout.

→ <<cset 1a44e61f2226>>

[Berk Duran]

References #492

Enabled the tap and hold actions for root goals.

→ <<cset b1a787153ecd>>

[Berk Duran]

References #492

ContributionController now finds the new layout container key element and sets it via a command.

ImpactDiagramView no longer keeps the local root (layout key) information, it gets this information from the key of the layout map entry.

ImpactModelElementView no longer keeps the local root (layout key) information, it gets this information from its ImpactDiagramView.

→ <<cset 8fd905ed0a1e>>

[Berk Duran]

References #492

Fixed the bug with setting a goal that already has a layout as a new root of a view.

→ <<cset 4b862b86e5d1>>

[Berk Duran]

References #492

Removed the commented out code in GoalImpactViewEditHandler.

→ <<cset 4891a1e553cf>>

[Berk Duran]

Merged in Issues/492-Root-Goal-creation-and-removal (pull request #116)

Resolves #492 - Root Goal creation and removal

Approved-by: Matthias Schoettle [e-mail]

→ <<cset 294a6573020c>>