Refact: Refactored code and removed liveVariable tests and its usage

[mnoman09]

Summary

• Refactored code and changed liveVariable to FeatureVariable and removed it from json
• Removed extra classes which were used by liveVariables
• Refactored ProjectConfig and removed passing of liveVariables

[coveralls]

Pull Request Test Coverage Report for Build 873

• 73 of 77 (94.81%) changed or added relevant lines in 9 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.5%) to 89.038%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
core-api/src/main/java/com/optimizely/ab/config/FeatureFlag.java	4	5	80.0%
core-api/src/main/java/com/optimizely/ab/config/FeatureVariable.java	2	3	66.67%
core-api/src/main/java/com/optimizely/ab/config/FeatureVariableUsageInstance.java	1	2	50.0%
core-api/src/main/java/com/optimizely/ab/config/parser/JsonConfigParser.java	23	24	95.83%

Files with Coverage Reduction	New Missed Lines	%
core-api/src/main/java/com/optimizely/ab/config/parser/JacksonHelpers.java	1	77.78%

Totals
Change from base Build 872:	-0.5%
Covered Lines:	2648
Relevant Lines:	2974

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💛 - Coveralls

[mikeproeng37]

lgtm

[thomaszurkan-optimizely]

LGTM