Prettify our error messages

[jmestxr]

Currently, our error messages are a little hard to read, and not very user-friendly in my opinion. E.g.

Some suggestions I thought of:

• make each error message as straightforward as possible, and deal with empty / edge cases. E.g. for the case of delete, we just print a one liner: "Deleted module[s]: CS1010". Remove the part where "Could not find Module[s] to delete".

Perhaps this is partly because the width of the CliScreen of the GUI is a little too narrow. To overcome this, we could add newlines (\n) to segregate relevant subsections of the error message, like how we do it in code.

Invalid command format!

add: Adds a module to the module list.

Parameters: 
/m <MODULE CODE>
/c <MODULE CREDITS>
...

Example:
add /m CS1101S /y Y1S1 ...

[Jun-How]

In addition to re-formatting all error messages, I will be including possible edge cases and slightly modifying the correct output messages to make them look more user-friendly. This may include changes to certain classes.