Integrate seco-base/kirkstone/develop_seco_setup

Commit: seco-base@ec8bfeb8

[seco-config] Added cloud config and nice level to menuconfig

Also fixed an error, where the sstate-dir wasn't set in the local.con.

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Commit: seco-base@1e6f763c

[seco-config] Clean-up and fixes to menuconfig

Removed empty entries, did some clean-up of the files and fixed a minor error in the environment submenu.