Add AttendanceEnum class

[yogtew]

Modify Person class to support Attendance field Added AttendanceEnum class Updated instances of Person object Modify SampleUtilData to include attendance for sample data Update Attendance and AttendanceTest Class to check for valid Attendance Modify PersonBuilder (to be improved in future commits) Storage (improved in future commits)

[yogtew]

Will be adding more commits to fix storage issues.

[coveralls]

Pull Request Test Coverage Report for Build 159

• 38 of 46 (82.61%) changed or added relevant lines in 7 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.06%) to 79.938%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/main/java/seedu/address/model/person/Person.java	12	13	92.31%
src/main/java/seedu/address/storage/XmlAdaptedPerson.java	4	6	66.67%
src/main/java/seedu/address/logic/parser/ParserUtil.java	0	5	0.0%
<!--	Total:	38	46	82.61%	-->

Totals
Change from base Build 148:	0.06%
Covered Lines:	1797
Relevant Lines:	2248

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💛 - Coveralls

[yogtew]

ready for review and merge