Implement DeleteZoomLinkCommand

[jonasngs]

Fixes #552

This PR implements a command to delete a zoom link from a module. Additionally, the user guide has been updated with the new feature.

The following classes were added:

1. DeleteZoomLinkCommand: executes the deletion of a zoom link from the module
2. DeleteZoomLinkParser: parsers the user input for a delete zoom link command

[michael-setia]

Added some trivial questions in the comments. Overall, LGTM.

[codecov-io]

Codecov Report

Merging #553 into master will decrease coverage by 0.21%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master     #553      +/-   ##
============================================
- Coverage     18.87%   18.66%   -0.22%     
  Complexity      370      370              
============================================
  Files           227      229       +2     
  Lines          4398     4448      +50     
  Branches        524      534      +10     
============================================
  Hits            830      830              
- Misses         3493     3543      +50     
  Partials         75       75              

Impacted Files	Coverage Δ	Complexity Δ
...ands/contactlistcommands/DeleteContactCommand.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...mmands/contactlistcommands/EditContactCommand.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...ommands/modulelistcommands/AddZoomLinkCommand.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...ands/modulelistcommands/DeleteZoomLinkCommand.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...a/seedu/address/logic/parser/ModuleListParser.java	48.27% <0.00%> (+4.52%)	10.00 <0.00> (ø)
...ic/parser/contactlistparsers/AddContactParser.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...ic/parser/modulelistparsers/AddZoomLinkParser.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...parser/modulelistparsers/DeleteZoomLinkParser.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...c/main/java/seedu/address/model/module/Module.java	15.65% <0.00%> (-0.14%)	4.00 <0.00> (ø)
.../java/seedu/address/model/module/ModuleLesson.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
... and 3 more

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