Modify EditCommand to accept NRIC instead of Index

[hweinian]

closes #56

Modified EditCommand to use nric instead of index.

Changes to delete: @yong-zhuo deleteCommand MESSAGE_INVALID_PERSON_DISPLAYED_INDEX messages was change to MESSAGE_PERSON_NRIC_NOT_FOUND

Test cases are disabled for the time being. It will be fixed in the next PR.

Let me know if there are any changes to be made!

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 93.33333% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../seedu/address/logic/parser/EditCommandParser.java	0.00%	2 Missing :warning:

Files with missing lines	Coverage Δ	Complexity Δ
src/main/java/seedu/address/logic/Messages.java	77.27% <ø> (-13.64%)	2.00 <0.00> (-1.00)
.../java/seedu/address/logic/commands/AddCommand.java	100.00% <100.00%> (ø)	8.00 <1.00> (ø)
...va/seedu/address/logic/commands/DeleteCommand.java	100.00% <100.00%> (ø)	7.00 <0.00> (ø)
...java/seedu/address/logic/commands/EditCommand.java	92.92% <100.00%> (-2.03%)	12.00 <2.00> (-1.00)
...java/seedu/address/logic/commands/FindCommand.java	100.00% <ø> (ø)	6.00 <0.00> (ø)
...java/seedu/address/logic/commands/ListCommand.java	100.00% <ø> (ø)	2.00 <0.00> (ø)
src/main/java/seedu/address/model/Model.java	100.00% <ø> (ø)	1.00 <0.00> (ø)
...rc/main/java/seedu/address/model/ModelManager.java	100.00% <100.00%> (ø)	24.00 <1.00> (+1.00)
...edu/address/model/person/NricMatchesPredicate.java	100.00% <100.00%> (ø)	6.00 <6.00> (?)
...c/main/java/seedu/address/model/person/Person.java	97.91% <ø> (ø)	25.00 <0.00> (ø)
... and 1 more

... and 6 files with indirect coverage changes