[FIX #853] "target+decoy" as targets

If a hit is a target+decoy then it will be considered as target.

modified:   ../src/openms/source/ANALYSIS/ID/FalseDiscoveryRate.cpp
modified:   ../src/tests/topp/FalseDiscoveryRate_output_1.idXML
modified:   ../src/tests/topp/FalseDiscoveryRate_output_2.idXML
modified:   ../src/tests/topp/FalseDiscoveryRate_output_3.idXML
modified:   ../src/tests/topp/FalseDiscoveryRate_output_4.idXML
[FIX #853] tests

added specific target+decoy class_tests

 	../src/tests/class_tests/openms/source/FalseDiscoveryRate_test.cpp
Merge pull request #855 from PetraGutenbrunner/fix-falsediscoveryrate

[FIX] FalseDiscoveryRate "target+decoy" hits should be considered as targets