Update DG overall styling to CS2101 standards

[eugene3231]

Update version number in MainApp.java

Introduction missing --> Revise it ✅
legend?
number the subheadings ✅
numbering (or bulletpoints all the way to be consistent) ✅
label diagrams to reference it ✅
write and document as you code

App vs app ✅

rest of the app contains four components -> use colon ✅
more consistent in sentence structure and type of word that it starts with. ✅

UNDOREDO -> active voice being used. ✅
no need to give explanation for the undoredo diagrams, quite self explanatory ✅

undo/redo design consideration: why did we choose alternative 2. Give a quick and simple reason. ✅
sentence structure for the pros/cons etc. Full sentence, or using of modals(will/may). Make it consistent ✅

Logic Component --> numbering ✅

[eugene3231]

Closing this issue as the DG problems listed above have been fixed by #101 and #111