Fix behaviour of edit person in loan view

[narwhalsilent]

Fix #120.

Behaviour changes:
When calling edit in loan view, the only things changed in GUI are the edited fields.

Code changes:

• Create new boolean property in ModelManager called isShownAllLoans.
• Refactor and overload ModelManager.updateFilteredLoanList().
• Change viewloan and edit to reflect the changes.

[codecov]

Codecov Report

Attention: Patch coverage is 25.00000% with 9 lines in your changes are missing coverage. Please review.

Project coverage is 47.02%. Comparing base (8b0e1d6) to head (60266ad).

Files	Patch %	Lines
...rc/main/java/seedu/address/model/ModelManager.java	42.85%	3 Missing and 1 partial ⚠️
...java/seedu/address/logic/commands/EditCommand.java	0.00%	2 Missing and 1 partial ⚠️
.../seedu/address/logic/commands/ViewLoanCommand.java	0.00%	1 Missing ⚠️
...seedu/address/logic/commands/ViewLoansCommand.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #124      +/-   ##
============================================
- Coverage     47.06%   47.02%   -0.04%     
- Complexity      433      434       +1     
============================================
  Files            99       99              
  Lines          2267     2271       +4     
  Branches        227      227              
============================================
+ Hits           1067     1068       +1     
- Misses         1155     1156       +1     
- Partials         45       47       +2     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[marcus-ny]

Changes lgtm!