Included a DateTimeFormatter formatter and LocalDate date

[kjiaxuan]

Added a LocalDate variable in Date.java
so dates are now not in string format unless use toString()

i think can use this to sort dates, or implement set feature (budget for a certain period of time etc)

[kjiaxuan]

#91

[geezlouisee]

Good job adding in the Date API! I think this will be useful when we want to implement most of our features. I also read somewhere that the API will help to ensure our time implementation to be immutable and hence, also thread-safe.

[JeremyLoye]

It is a good idea to implement a LocalDate object for our dates. Do consider some revisions in implementation though:
The isValidDate method currently has repeat checks namely the check of test string with VALIDATION_REGEX and the LocalDate parse check. Possible to remove the regex with current implementation.

[eugeneyl]

Adding the DateTimeFormatter will help in preventing the input of strings that are not actually date and prevent confusion during the implementation.