Cleanup repo

[papataco14]

• Removed redundant images and tutorial
• Renamed addressbook.json to companydata.json for clarity when referencing in UG for FAQ (will update UG later)
• Removed all traces of undo command feature in DG (including images and diagrams)

[codecov[bot]]

Codecov Report

Merging #258 (53be868) into master (da6d6fe) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master     #258   +/-   ##
=========================================
  Coverage     73.72%   73.72%           
  Complexity      579      579           
=========================================
  Files            87       87           
  Lines          1907     1907           
  Branches        220      220           
=========================================
  Hits           1406     1406           
  Misses          422      422           
  Partials         79       79           

Files	Coverage Δ
src/main/java/seedu/address/model/UserPrefs.java	80.00% <100.00%> (ø)