Inconsistent baseDiv in CLI and VS Code extension

[NiklasRentzCAU]

Currently the VS Code extension uses the baseDiv for Sprotty of "keith-diagram_sprotty", whereas the CLI uses just "sprotty", potentially causing inconsistencies between both executables, see e.g. #178. Furthermore, the "keith-diagram" string is still a somewhat magic string around the code base. Both implementations should use the same base ID and no magic strings for this, but rather read it from the options, as was done to fix the issue in #178 as well.