restructured the calvin_navigation repository

the following was done:
* duplicate configs and launch files were removed
* redundant sub packages were merged together:

there's

a)calvin_navigation now, which holds the configs and .launchs for the 3rd party navigation-related components (amcl, move_base, gmapping, frontier_exploration)
and offers .launch for navigation behaviors in different setups (2d slam, navigation with one or two maps)

b) calvin_navigation_experiments, which holds the map data and high-level launchfiles to launch calvin's navigation in a specific environment

c) the calvin_map_server wasn't touched since it is not maintained right now, however the dependencies had been changed to match a) and b)

* the move_base configs for gmapping and amcl had been merged, since there was no obvious reason to use different setups and during test the unified setup performed fine.
however this might be a potential cause later on, here's what has changed:

Before this commit, there were a few differences between the move_base
and costmap_2d configurations when using AMCL vs. gmapping. Now, we're
using the AMCL values for everything:

i) gmapping's global_costmap_params.yaml had the additional param
  `unknown_cost_value: 255`
ii) gmapping's move_base config had a few additional parameters, which
  are now commented out in the following files:

        calvin_navigation/config/move_base_params.yaml
        calvin_navigation/config/recovery_behaviors.yam
removed calvin_bringup and calvin_gazebo deps

we will probably not use launchfiles that both launch a bringup (+gazebo) and the navigation, since this prevents restarting one or the other
therefore it's enough to depend on calvin_navigation and provide the repective map data