Consolidate all visualize code in single directory

[thomasneirynck]

The code for Visualize is currently very fragmented.

• core_plugins (visualization utilties/implementations)

  • kbn_vislib_vis_types
  • markdown_vis
  • metrics
  • region_map
  • tagcloud
  • tile_map
  • region_map
  • table_vis
  • timelion
  • kibana/visualize (landing page of the app)

• ui/public (utility-code)

  • vis
  • vislib
  • visualize
  • agg_configs
  • agg_response

Consider a more sensible reorganization.
e.g.:
- Move all reusable code to ui/public under single directory.
- Move all plugin code under single 'visualizations' directory in core_plugins
- retain visualize landing page under kibana/visualize

[thomasneirynck]

It's probably too late to do this for 6.0. It's a big reorganization, with some major internal impact.

[timroes]

No longer relevant in the new Kibana Platform.