Update UG, DG, PPP and README

[yeo-kexin]

UG

• Edit documentation for list and update pictures for TagEdit

DG

• Update UML diagrams for Model and Storage
• Include documentation for taskclear

README

• Update UI picture

[codecov-io]

Codecov Report

Merging #251 (16084aa) into master (57bb522) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master     #251   +/-   ##
=========================================
  Coverage     70.40%   70.40%           
  Complexity      658      658           
=========================================
  Files           106      106           
  Lines          2139     2139           
  Branches        243      243           
=========================================
  Hits           1506     1506           
  Misses          579      579           
  Partials         54       54           

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[siqiang-ng]

Overall lgtm, but for ur ppp I think it exceeds the 2 pages limit so Im not sure if you want to cut down here

[khinkhinn]

lgtm