add unenroll command

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 57 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...tahub/contacts/logic/commands/UnenrollCommand.java	0.00%	41 Missing :warning:
...b/contacts/logic/parser/UnenrollCommandParser.java	0.00%	15 Missing :warning:
...tahub/contacts/logic/parser/AddressBookParser.java	0.00%	1 Missing :warning:

Files with missing lines	Coverage Δ	Complexity Δ
src/main/java/tahub/contacts/logic/Messages.java	71.42% <ø> (ø)	4.00 <0.00> (ø)
...hub/contacts/logic/parser/EnrollCommandParser.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...tahub/contacts/logic/parser/AddressBookParser.java	72.41% <0.00%> (-2.59%)	14.00 <0.00> (ø)
...b/contacts/logic/parser/UnenrollCommandParser.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...tahub/contacts/logic/commands/UnenrollCommand.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)

[FlyingDonkeys]

Done with enroll command