TitelMake cmk --keepalive reload possible without execv

The complete restart of the keepalive processes creates a lot of load when multiple ones are performing the restart at the same time. We should rewrite the "reload config" mechanism to a real reload using a dedicated function within Check_MK. To make this possible, we need to know which variables are config values and which are not. Then we need to precompile the whole config incl. hard coded and user config in a dedicated file. This file is being created during "activate changes" and read during each start of the keepalive processes.