[doc] css other browsers

https://developer.mozilla.org/en-US/docs/CSS/linear-gradient#Cross-browser_gradients
[doc] Rework the adding_component doc

- Some stuff has been moved to new_middleware
- Document _name, _short_descr, add_data, add_property with several
  examples
- Remove blender part that are now false
- TODO Write the builder part

Important progress to #289
[human] Completed adaptation for new builder-naming
[builder] Make sure that unparent_wheel is automatically called
[doc] Add a tag for moos
[doc] Rewrite new_middleware

- explicit how to add datastream handler in the class based method
- Provide specific explanation for each middleware, with various
  examples
- document how to add a datastream manager

XXX: maybe we must split it in two ?
XXX: write MOOS specific stuff when it is ready. See #275

Still, it fixes #281