Improve our client-side error handling

[NicMcPhee]

Our client-side error handling really isn't great, and that tends to lead to their error handling also not being great.

As an example, if you put a random ID in the URL for a user (e.g., http://localhost:4200/users/badID) you don't get any kind or error message or useful feedback – you just get a blank user page:

This is clearly not awesome. There should be some kind of message there that gives the user some info about what's going on, and probably some kind of console.log() message about the problem to help with debugging.

This will carry through to Lab 4 and the iteration template.

This may be related to #761, as turning on strict mode in TS will flag a lot of these issues for us.

[NicMcPhee]

I think this has been resolved by various commits over the past couple of years.