Modify dateOfLastVisit to use LocalDate instead of String

[rayray39]

This PR completed the following things

1. update internal representation of DateOfLastVisit to be LocalDate instead of a String.
2. restricts the date of last visit to be no later than today's date (i.e., the user will not be able to add a contact with a date of last visit that is either tomorrow or later).

closes #141
closes #166

[codecov]

Codecov Report

Attention: Patch coverage is 55.55556% with 12 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
...a/seedu/address/model/person/PersonComparator.java	20.00%	6 Missing and 6 partials ⚠️

Files with missing lines	Coverage Δ	Complexity Δ
...va/seedu/address/model/person/DateOfLastVisit.java	96.00% <100.00%> (+0.34%)	11.00 <6.00> (+2.00)
...a/seedu/address/model/person/PersonComparator.java	50.00% <20.00%> (-38.89%)	5.00 <0.00> (ø)

... and 11 files with indirect coverage changes

[AbdulrahmanAlRammah]

Overall good changes, but I have some concerns regarding the testing. Please see comments.

[AbdulrahmanAlRammah]

I don't quite understand the ensure month is 01-12 comment. Do you mean ensure that month is after day?

Edit: Oh I think you mean ensure the month is typed with 2 digits, but I think you can take this as a given since we requested dd-MM-yyyy format. You can say "Date of Last Visit should be in exactly dd-MM-yyyy format. Also it is good to add an example in the error message.

[rayray39]

yup that was the intention and i will update the error message as suggested

[AbdulrahmanAlRammah]

It may be better to not change this. The LATEST_VALID_DATE is meant to distinguish entries with no date of last visit from those that do have. I believe in this case if you set the date of last visit to be today for one of the entries and then sort the entry with dolv as today will be mixed with those without date of last visit. Hence, it is better to keep the value as is or to set it as today + 1.

[rayray39]

DateOfLastVisit has been updated to accept a date no later than today, which means that a date of "31-12-9999" would not be possible. I have updated the comparators for date of last visit to not use EARLIEST_VALID_DATE and LATEST_VALID_DATE. Although this makes the code slightly longer and less clean, the functionality works as expected.

[AbdulrahmanAlRammah]

LGTM