Add storage for concertContact

[wes-w-z-h]

• [x] add & delete from storage
• [ ] tests

Fixes #78

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 75.00000% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...edu/address/storage/JsonAdaptedConcertContact.java	69.23%	2 Missing and 2 partials :warning:
...u/address/storage/JsonSerializableAddressBook.java	81.81%	1 Missing and 1 partial :warning:

Files with missing lines	Coverage Δ	Complexity Δ
...java/seedu/address/storage/JsonAdaptedConcert.java	100.00% <ø> (ø)	9.00 <0.00> (ø)
...u/address/storage/JsonSerializableAddressBook.java	94.44% <81.81%> (-5.56%)	7.00 <0.00> (+1.00)	:arrow_down:
...edu/address/storage/JsonAdaptedConcertContact.java	69.23% <69.23%> (ø)	3.00 <3.00> (?)

... and 4 files with indirect coverage changes

[wes-w-z-h]

should we do that in a new issue instead since it's quite big