Implement Profile pic

[ChooJeremy]

Implement uploading of profile pic of employees.
Supports #66

[coveralls]

Pull Request Test Coverage Report for Build 702

• 37 of 41 (90.24%) changed or added relevant lines in 5 files are covered.
• 10 unchanged lines in 3 files lost coverage.
• Overall coverage decreased (-0.2%) to 86.815%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/main/java/seedu/address/logic/parser/AddressBookParser.java	0	1	0.0%
src/main/java/seedu/address/logic/commands/ProfilePicCommand.java	31	34	91.18%

Files with Coverage Reduction	New Missed Lines	%
src/main/java/seedu/address/storage/XmlAdaptedPerson.java	1	99.12%
src/main/java/seedu/address/storage/XmlArchiveListStorage.java	2	63.64%
src/main/java/seedu/address/model/util/SampleDataUtil.java	7	72.41%

Totals
Change from base Build 663:	-0.2%
Covered Lines:	2930
Relevant Lines:	3375

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💛 - Coveralls