Prevent malicious manual updating of save file

[drustanyjt]

This PR closes #144 .

Mainly removes occurrences of tags that caused potential issues in the save file.

[codecov]

Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 70.02%. Comparing base (d3482fd) to head (ae1a2b5).

Files	Patch %	Lines
src/main/java/seedu/address/logic/Messages.java	0.00%	1 Missing ⚠️
...c/main/java/seedu/address/model/person/Person.java	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #152      +/-   ##
============================================
- Coverage     70.68%   70.02%   -0.66%     
+ Complexity      499      492       -7     
============================================
  Files            81       81              
  Lines          1733     1715      -18     
  Branches        175      171       -4     
============================================
- Hits           1225     1201      -24     
- Misses          439      445       +6     
  Partials         69       69              

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[tengcharmaine]

LGTM!