Added calculation to determine discordant couples.
Merge with upstream

Merge branch 'master' of github.com:I-TECH/openmrs-module-kenyaemr into experimental
Minor code clean up. Removed redundant code.
Added MOH 731 PMTCT indicator HV02-12
Added WHO staging and CD4 fields in the MCHMS antenatal visit form
Minor code fix
Added calculations and cohorts to calculate MOH 731 PMTCT indicators HV02-18 to HV02-20
Merge with upstream after conflic resolution
Added test class for AssessedOnFirstVisitCalculationTest.java
Added test for MchmsFirstVisitDateCalculation
Merge branch 'master' of github.com:I-TECH/openmrs-module-kenyaemr

Merge with upstream
Merge pull request #69 from gitahi86/master

Added MOH 731 PMTCT Indicators HV02-12 and (HV02-18 to HV02-20)