Fix edit commmand bugs

[abdurrahmanfaqihiskandar]

Fixed 2 bugs:

1. Editing other fields does not change the student's details in the training panel
2. Changing one dismissal time to conflict with one training session, will make the other training
   sessions disappear from the GUI

[codecov-io]

Codecov Report

Merging #98 into master will decrease coverage by 0.13%.
The diff coverage is 46.15%.

@@             Coverage Diff              @@
##             master      #98      +/-   ##
============================================
- Coverage     69.21%   69.07%   -0.14%     
  Complexity      664      664              
============================================
  Files           108      108              
  Lines          2212     2225      +13     
  Branches        261      262       +1     
============================================
+ Hits           1531     1537       +6     
- Misses          579      585       +6     
- Partials        102      103       +1     

Impacted Files	Coverage Δ	Complexity Δ
...n/java/seedu/canoe/logic/commands/EditCommand.java	79.38% <36.36%> (-3.95%)	12.00 <0.00> (ø)
...java/seedu/canoe/logic/commands/DeleteCommand.java	76.19% <100.00%> (+1.19%)	7.00 <0.00> (ø)
src/main/java/seedu/canoe/model/Model.java	100.00% <100.00%> (ø)	1.00 <0.00> (ø)

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[yejiadong]

LGTM.