Edit help window

[nweiyue]

Update help window to contain all commands.
Future styling can be implement.

[codecov-io]

Codecov Report

Merging #101 into master will increase coverage by 0.16%.
The diff coverage is 0.00%.

@@             Coverage Diff              @@
##             master     #101      +/-   ##
============================================
+ Coverage     71.15%   71.32%   +0.16%     
- Complexity      650      655       +5     
============================================
  Files           109      109              
  Lines          2063     2068       +5     
  Branches        224      225       +1     
============================================
+ Hits           1468     1475       +7     
+ Misses          528      525       -3     
- Partials         67       68       +1     

Impacted Files	Coverage Δ	Complexity Δ
...logic/commands/sessionlist/EditSessionCommand.java	85.71% <ø> (ø)	14.00 <0.00> (ø)
...ogic/commands/sessionlist/EnterSessionCommand.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...a/atas/logic/commands/studentlist/EditCommand.java	96.87% <ø> (ø)	13.00 <0.00> (ø)
src/main/java/atas/ui/HelpWindow.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
src/main/java/atas/storage/JsonAdaptedSession.java	72.09% <0.00%> (-3.52%)	8.00% <0.00%> (ø%)
src/main/java/atas/model/attendance/Session.java	89.06% <0.00%> (+0.17%)	26.00% <0.00%> (ø%)
.../main/java/atas/storage/JsonAdaptedAttributes.java	64.00% <0.00%> (+5.66%)	10.00% <0.00%> (+1.00%)
src/main/java/atas/model/attendance/Presence.java	63.63% <0.00%> (+9.09%)	7.00% <0.00%> (+1.00%)
...main/java/atas/model/attendance/Participation.java	63.63% <0.00%> (+9.09%)	7.00% <0.00%> (+1.00%)
...rc/main/java/atas/model/attendance/Attributes.java	80.95% <0.00%> (+9.52%)	10.00% <0.00%> (+2.00%)

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[erisjacey]

LGTM