polenaRT: installer upgrades, independend builds

[flhofer]

The following changes should be implemented

• detection of used kernel version - and distro - and verification if we have a kernel config file for that
• if not, proposal of kernel version from vanilla source, close to the actual, config merge with installed /boot/config*
• if user does not want to build a kernel for this system (or distro), specified parameter gives also system, e.g. alpine-x86_64-6.1.75 ecc, and we run a container with that environment, install packages and build kernel, if needed
• test run in container, always
• screen option