Support for correspondence estimation with different point types

[SergioRAgostinho]

Fixes #329. Credits for @aichim, @jpapon and @taketwo . Added unit test for XYZ point types.

Still have some doubts:

• pcl::registration::CorrespondenceEstimation seems to support with all point types. Is it supposed to work with more weird cases of source and target point types, e.g. between XYZ points types <-> Normal point types? Not sure if this is possible.
• Should I also add a test for Normal point types? RGB? Is KDTree flexible enough for this?