Clean up repo branching [#2741809]

It would be great to have all feature branches into one location.

I would propose using a Gitflow like structure

- 5.x-1.x
- 6.x-2.x
- 7.x-3.x
- 7.x-4.x
- features
  - 2610122-circular-dependencies
  - 2702715-server-views-handler
  - 2704247-hostmaster-get-nid
  - 2705073-guarded-nodes-hook
  - 2705093-hook-view
  - 2705097-server-verify-platforms
  - 2705713-node-pages
  - 2709565-server-db-select
  - 2709593-rename-example-drush-file
  - 2713239-hook-validate-state
  - 2714539-vertical-tabs-services
  - 2714561-hostingService-name
  - 2714569-service-required
  - 2731472-backup-delete-warnings
  - 6.x-2.x-backports
  - 7.x-3.x-1995506
  - 7.x-3.x-2694037
  - dev-2223033
  - dev-2359571
  - dev-decoupling
  - dev-sni
  - dev-ssl-ip-allocation-refactor
  - dev/1212086
  - dev/1895580-task-priorities
  - dev/2000964-ip-allocation-clusters
  - dev/2212149
  - dev/2685931
  - dev/2714049-parallel-queue
  - dev/2725825-hosting-gc
  - dev/2729279
  - dev/2730603-hook_entity_property_info
  - dev/hosting-import-dbname
  - dev/packages-count
  - dev/site-count
  - dev/subfolders
  - field-extra-fields
  - issue-2446749-hosting-task-status

and all feature branches into same structure: issue#, dash, short dashed description