Add edit functionality for role

[karthickkc]

Added edit functionality for role Added tests to ensure it's working fixes #44

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Files with missing lines	Coverage Δ	Complexity Δ
...java/seedu/address/logic/commands/EditCommand.java	96.47% <100.00%> (ø)	13.00 <0.00> (ø)
.../seedu/address/logic/parser/EditCommandParser.java	93.10% <100.00%> (+0.51%)	12.00 <0.00> (+1.00)

... and 2 files with indirect coverage changes