allow user to enable/disable specific Higgs 2-loop corrections
add default Higgs 2-loop corrections to SLHA files
shorten description of FlexibleSUSY block entry 11
correcting comment
initialize Higgs 2-loop correction struct
impelemt if-statements which select the Higgs 2-loop correctons
define abbreviations for Slavich 2-loop Higgs function names
replace original Higgs 2-loop function calls by readable abbreviations
update ChangeLog
Merge branch 'feature-higgs-2loop-flags' into development