UG Guide Improvements

[HanB1n]

Update the JAR File Link.
Remove all symbols of AB3
Update the screenshot of Help function

[HanB1n]

Edit headers to be more presentable and segregated
Make the examples relevant to our use case, remove the Prison stuff

[tingxuanp]

Update command summary
Make language more user-centric
Could have more step by step guidance for using the addressbook initially
Even things like the meaning of tags need to be explicitly stated from the beginning

[HanB1n]

Fix hyperlinks

[tingxuanp]

Introduction: explicitly identify target users, assumptions, user-centric description of the product
give more examples for all commands

update screenshots

[tingxuanp]

Make layout more suitable for skimming and scanning, more spacing etc

could consider colour coding the features to make it easier to read?

[tingxuanp]

Update use cases examples for new commands