Implement EditZoomLinkCommand

[jonasngs]

Fixes #554

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

The following classes were added:

1. EditZoomLinkCommand: to execute the command to edit a zoom link
2. EditZoomLinkParser: to parse the user input
3. EditZoomDescriptor: class to encapsulate details of the edited zoom link and the module lesson that contains the zoom link to be edited

[codecov-io]

Codecov Report

Merging #555 into master will decrease coverage by 0.51%.
The diff coverage is 8.46%.

@@             Coverage Diff              @@
##             master     #555      +/-   ##
============================================
- Coverage     18.89%   18.37%   -0.52%     
- Complexity      370      375       +5     
============================================
  Files           227      233       +6     
  Lines          4392     4538     +146     
  Branches        524      548      +24     
============================================
+ Hits            830      834       +4     
- Misses         3487     3626     +139     
- Partials         75       78       +3     

Impacted Files	Coverage Δ	Complexity Δ
...main/java/seedu/address/commons/core/Messages.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...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> (?)
...commands/modulelistcommands/EditModuleCommand.java	18.91% <0.00%> (ø)	3.00 <0.00> (ø)
...ommands/modulelistcommands/EditZoomDescriptor.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...mmands/modulelistcommands/EditZoomLinkCommand.java	0.00% <0.00%> (ø)	0.00 <0.00> (?)
...modulelistcommands/ViewArchivedModulesCommand.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...ic/parser/contactlistparsers/AddContactParser.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
... and 21 more

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[michael-setia]

Added few comments but overall, LGTM.