Add emojis to command output, edit UG

[ruoyann]

Problems:

• When changing to dark theme, emojis can appear weird as shown below:
• Emojis slightly cut off especially for the clock emoji

Improvements

• Studied hours still in text form. Any emojis we can use to replace that?

[codecov-commenter]

Codecov Report

Merging #169 (9c474c7) into master (cbbf63a) will increase coverage by 0.08%. The diff coverage is 77.14%.

@@             Coverage Diff              @@
##             master     #169      +/-   ##
============================================
+ Coverage     62.51%   62.60%   +0.08%     
- Complexity      670      673       +3     
============================================
  Files            94       94              
  Lines          2580     2599      +19     
  Branches        335      337       +2     
============================================
+ Hits           1613     1627      +14     
- Misses          868      873       +5     
  Partials         99       99              

Impacted Files	Coverage Δ
.../java/seedu/address/model/studyspot/Favourite.java	75.00% <0.00%> (-25.00%)	:arrow_down:
.../java/seedu/address/model/studyspot/StudySpot.java	90.47% <75.00%> (-1.84%)	:arrow_down:
...main/java/seedu/address/model/amenity/Amenity.java	90.47% <100.00%> (ø)
...ain/java/seedu/address/model/studyspot/Rating.java	90.00% <100.00%> (+10.00%)	:arrow_up:
src/main/java/seedu/address/model/tag/Tag.java	100.00% <100.00%> (ø)

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