Fix various bugs with undo/redo, addvisit and reorganized parts of UG

[eugene3231]

Fix bugs with

1. undo/redo and addvisit editvisit and deletevisit,
2. addvisit with vd/
3. prescription and diagnosis mixup

Also increased clean startup cliniCal.jar window size

Also reorganized entire UG structure and shifted undo/redo into general commands
Also added a table for formatting legend after Introduction

[codecov]

Codecov Report

Merging #173 into master will increase coverage by 0.16%.
The diff coverage is 62.06%.

@@             Coverage Diff              @@
##             master     #173      +/-   ##
============================================
+ Coverage     63.10%   63.27%   +0.16%     
- Complexity      761      764       +3     
============================================
  Files           119      119              
  Lines          2889     2905      +16     
  Branches        344      345       +1     
============================================
+ Hits           1823     1838      +15     
- Misses          957      958       +1     
  Partials        109      109              

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/seedu/address/MainApp.java	0.00% <0.00%> (ø)	0.00 <0.00> (ø)
...n/java/seedu/address/commons/core/GuiSettings.java	69.23% <ø> (ø)	5.00 <0.00> (ø)
...main/java/seedu/address/commons/core/Messages.java	0.00% <ø> (ø)	0.00 <0.00> (ø)
...dress/logic/commands/AddProfilePictureCommand.java	36.66% <0.00%> (ø)	3.00 <0.00> (ø)
.../seedu/address/logic/commands/AddVisitCommand.java	63.15% <ø> (+3.15%)	7.00 <0.00> (ø)
...java/seedu/address/logic/commands/RedoCommand.java	100.00% <ø> (ø)	3.00 <0.00> (ø)
...seedu/address/logic/commands/SaveVisitCommand.java	44.44% <0.00%> (-4.34%)	10.00 <0.00> (ø)
...java/seedu/address/logic/commands/UndoCommand.java	100.00% <ø> (ø)	3.00 <0.00> (ø)
...ic/commands/appointment/AddAppointmentCommand.java	50.00% <0.00%> (-1.22%)	8.00 <0.00> (ø)
...ava/seedu/address/logic/parser/CliniCalParser.java	65.51% <ø> (ø)	15.00 <0.00> (ø)
... and 9 more

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[Michaeliaaa]

LGTM!