Rewrite gever setup

  - Introduce two zcml directives to configure deployments and ldap profiles.
  - Simplify deloyment form, remove multi-client configuration options.
  - Add custom setuphandlers for local roles, initial repository and document templates.
  - Configure development options and add environment variable to enable them easily.
  - Update branding, add onegovgever logo.

Closes #368
@deiferni @phgross just FYI: This change means we need to update the ZCML directives in the respective policies first before we can even boot the instance with this version of `opengever.core`.