Update .travis.yml

Let's include release branch (dart_3.0).
Move flann include out of header file. Reduce flann to a build dependency.

Flann is no longer required for using DART, instead it is only required for building it.
Merge branch 'master' of github.com:dartsim/dart
Fix compiler error caused by last commit
Update .travis.yml
Update .travis.yml
Adapt Cmake files for FLANN only being a build dependency
Set version to 2.6
Update .travis.yml

Include refactoring branch which will be merged to master branch for dart 3.0
Refactor DART. Lots of non-backwards-compatible changes.

- Remove Transformation classes. Their functionality is now included in joint classes.
- Add Featherstone algorithm. Can currently only be used without collision handling. The old algortihm is still present and used for that case.
- Remove kinematics namespace. Functionality is moved to dynamics classes.
- Add dart root namespace
- A lot of function and variable renames
- Add constraint namespace
- Some parsers, unit tests and apps have not been adapted to the changes yet and are therefore currently excluded from building.
- Add "common" namespace
Change #if _DEBUG to #ifndef NDEBUG
Update .travis.yml
Remove deprecated functions.
Remove #include "common/Deprecated.h" in Skeleton.h.
Fix compiler error on Windows
Remove unused variables: mRestitutionCoeff, mFrictionCoeff.
Fix compiler error caused by last commit
Remove "using namespace std" from headers. Fix issue #73.
Fix #4. Rename M_EPSILON to DART_EPSILON to prevent confliction with external M_EPSILON.
Fix compiler error caused by last commit