Fixed an error in Function CartesianCoordinates::weightedCenter

The calculation of the center of mass was incorrect. The prefactor was
1/(N*M), now it is 1/M
added missing boost components
added missing boost component
made the format of output-xyz-files more pretty

the atomic coordinates are now written as fixed-width numbers
with five decimal places
Merge pull request #33 from janvc/master

Fixed cmake problems and a fault mentiond in the issues