add comments describe functions in every interpolation method class

gui/manual/gui_manual_v1_2_1.tex

...mpimet/yacgui/xml/interpolation/AverageInterpolation.java

...t/yacgui/xml/interpolation/ConservativeInterpolation.java

...met/yacgui/xml/interpolation/FixedValueInterpolation.java

...cgui/xml/interpolation/NNearestNeighborInterpolation.java

.../yacgui/xml/interpolation/PatchRecoveryInterpolation.java

...xml/interpolation/SmoothedPatchRecoveryInterpolation.java

...pimet/yacgui/xml/interpolation/UserFileInterpolation.java