Implement UnassignCommand

[florenciamartina]

Fixes #100

[codecov-io]

Codecov Report

Merging #114 into master will increase coverage by 0.28%.
The diff coverage is 60.37%.

@@             Coverage Diff              @@
##             master     #114      +/-   ##
============================================
+ Coverage     73.77%   74.06%   +0.28%     
- Complexity      655      692      +37     
============================================
  Files           102      106       +4     
  Lines          1880     1951      +71     
  Branches        220      230      +10     
============================================
+ Hits           1387     1445      +58     
- Misses          428      435       +7     
- Partials         65       71       +6     

Impacted Files	Coverage Δ	Complexity Δ
...main/java/seedu/address/commons/core/Messages.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
.../seedu/address/logic/parser/AddressBookParser.java	81.48% <0.00%> (-3.14%)	18.00 <0.00> (ø)
src/main/java/seedu/address/model/Model.java	100.00% <ø> (ø)	2.00 <0.00> (ø)
...rc/main/java/seedu/address/model/ModelManager.java	87.83% <0.00%> (-2.31%)	32.00 <0.00> (+1.00)	⬇️
...c/main/java/seedu/address/model/module/Module.java	81.08% <25.00%> (-6.80%)	18.00 <1.00> (+1.00)	⬇️
src/main/java/seedu/address/model/AddressBook.java	70.58% <33.33%> (-2.33%)	19.00 <1.00> (+1.00)	⬇️
...a/seedu/address/model/module/UniqueModuleList.java	66.66% <55.55%> (+1.58%)	26.00 <2.00> (+4.00)
.../seedu/address/logic/commands/UnassignCommand.java	73.91% <73.91%> (ø)	10.00 <10.00> (?)
...du/address/logic/parser/UnassignCommandParser.java	80.00% <80.00%> (ø)	2.00 <2.00> (?)
.../seedu/address/logic/parser/FindCommandParser.java	86.84% <0.00%> (-2.91%)	16.00% <0.00%> (-1.00%)
... and 11 more

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[justintzuriel]

Minor change, other than that LGTM