Add support for 'morse import <path>'

This allows to import pre-existing simulations in MORSE
for later run them with 'morse run' (or 'morse edit').

'path' must be a local path.

Partially fix #396
[doc] Added a 'quickstart' tutorial

It illustrates to use of 'morse create' and friends.

Partially fix #396
Implement a template for sensors

Used when calling 'morse add sensor ...'

Partially fix #396
[doc] Document in more places 'morse create|add'

Related to issue #396
Removed non-standard ROS serialization for KUKA joints

Originally introduced in #301. The normal way to add custom
serialization is now with 'add_stream'. Cf
http://www.openrobots.org/morse/doc/latest/user/builder.html#middleware-configuration