mbeddr platform requires jetbrains.mps.ide.devkit because of c.m.m.dataflow

[sergej-koscejev]

If an RCP includes the entire mbeddr platform but excludes the jetbrains.mps.ide.devkit plugin (plugins/mps-devkit), it will not start because com.mbeddr.mpsutil.dataflow plugin requires the MPS devkit.

This is not ideal because the devkit contains UI actions to develop new DSLs and an RCP shouldn't require it.

It can be fixed in the RCP build script by excluding the com.mbeddr.mpsutil.dataflow plugin from the platform but perhaps we should consider splitting our distribution into "runtime part", to be included in the RCP, and "design time part", to be used during development only, with the latter depending on the former but not vice versa.