Streamline headers included in task base

The main change is to remove the inclusion of the all-encompassing Types.hpp header in TaskBase.hpp

This saves both CPU time and memory during the build. On
control/orogen/auv_control, which only imports the 'base' typekit,
we save on my (very old Core 2 Duo) machine 1min 20s and 250M of
memory (benchmark done with -j1). On -j4, this would mean roughly
1G of memory.

In addition, it avoids unnecessarily rebuilding task files. The
Types.hpp headers include all types of a typekit, as well as the
imported typekits, which means that we currently MUST rebuild all
task files as soon as a single header is modified in e.g. base/types.

BACKWARD INCOMPATIBILITY: since a lot less headers are included, the user-facing
code in Task.cpp / Task.hpp cannot assume that all types are available
anymore. This does include typedefs that are used in the orogen file.
All types must be manually included in Task.hpp. For instance,
as base::commands::Joints is a typedef, one would need to include
base/commands/Joints.hpp explicitly even if there is a port of type
base::commands::Joints on the task. I personally think that it is
worth it.

RAW DATA

Command being timed: "make -C build/tasks"

Without this commit:
  User time (seconds): 249.27
  System time (seconds): 16.02
  Percent of CPU this job got: 99%
  Elapsed (wall clock) time (h:mm:ss or m:ss): 4:27.81
  Maximum resident set size (kbytes): 893588

With the patch:
  User time (seconds): 176.46
  System time (seconds): 12.16
  Percent of CPU this job got: 99%
  Elapsed (wall clock) time (h:mm:ss or m:ss): 3:09.72
  Maximum resident set size (kbytes): 640356