Import/Export DPU configuration in Dialog

[jakubklimek]

Add a tab to DPU dialog (usable for all DPUs) which displays serialized configuration string so that it can be copy&pasted.

[skodapetr]

This change is not well specified (invalid configuration, version control, etc .. ) and probably not necessary for Core DPUs. An alpha implementation is in mff-uk repository as a DPU add-on.