Set up maven build of core, plugins, dashboard, assembly

Added maven build of submodules.
Removed duplicated resources
CODE_OF_CONDUCT, CONTRIBUTING, Dockerfile, LICENSE, NUMBERING, README - all move to root please.
Set up default maven JVM config
Moved dependency management from che-dependcies for che dependencies. Theard party dependecies left in che-dependecies
Removed unused travis cunfigs
Removed outdated scm configs

Signed-off-by: Sergii Kabashniuk <skabashnyuk@codenvy.com>

Author: Sergii Kabashniuk