added installation instruction for docker image
Merge pull request #1133 from crate/h/docker-installation

added installation instruction for docker image
added graceful_stop cluster settings
documentation for graceful_stop cluster settings
implemented rounting.allocation.enable setting
test fixup
changed implementation of global settings
added cluster upgrade settings to crate.yml
added docu for extended cluster settings
moved settings documentation from reference to documentation
added missing configuration settings description
to crate.yml
implemented mostly all dynamic cluster setting expressions
fixed setting object settings
added missing settings to documentation
added missing settings to crate.yml