Added a CATKIN_IGNORE marker in the template and remove it in create_rtt_pkg

The patch makes sure that catkin does not find the `package.xml` in the `rtt_roscomm_pkg_template` folder for any reason, neither in the package source nor in devel-space nor in install-space.

This is required if the devel-space is located within the source folder, which in general is possible. Otherwise the template is found as package (with a broken `package.xml`) when cmake is executed the 2nd time after the template has been copied to devel-space.