Include visual editor as part of functionality of soletta-dev-app

[lblim]

Visual editor is a good feature to enable users to create applications by drag and drop the nodes (such as Node-RED), create links etc. Currently, soletta-dev-app only allows application to be written using FBP scripts. The nodes diagram is constructed and shown to the users based on the FBP scripts.

The project https://github.com/solettaproject/soletta-visual-editor becomes dormant now
solettaproject/soletta-visual-editor#11

[lblim]

@laykuanloon @fulong82 @elvinongbl