Implement a form based REST DSL editor

[lhein]

Create a form based editor that lets users design their REST definition similar to what we had in the Fuse IDE. Gather ideas also with our own Apicurio / Apicurito. This editor should also allow users to import an OpenAPI spec via file or URI reference. On import we let the user decide wether they want to only have the routes, the rest routes or both.

Part of the import functionality does already exist in VS Code tooling.

[lhein]

relates to #54

[lhein]

see https://access.redhat.com/documentation/en-us/red_hat_fuse/7.2/html-single/tooling_user_guide/index#viewing_a_graphical_representation_of_rest_dsl_components