Limit nick length and whitespaces in UI

[pastly]

Fixes #337.

Max nick length of 24 was chosen arbitrarily.

It seemed necessary to make changes in both ContactUser.cpp and UserIdentity.cpp even though only the changes in ContactUser.cpp seemed to have any affect.

[s-rah]

I think the spirit of the change is fine - however, I think 24 is too short. As a usecase, I have many ricochet contacts who I reference by name(@twitter handle) - even taking by name only just makes the cut - "Sarah (@SarahJamieLewis)" and there are a fair few of my contacts who would be truncated by this change.

With the simplification removing the troubling whitespace, the only time that length is an issue is in the "...is online/offline" display, truncating it at this UI point might be a nicer solution, without having to make arbitrary decisions about name length.

[pastly]

Now it only makes changes to what is displayed. In this order:

• repeated whitespace characters are squashed into a single space
• leading and trailing whitespace is removed
• truncated to the first 80 characters

[special]

These limits sound reasonable.

We shouldn't be changing the nickname at display-time, though. We'll end up having to copy this code to a lot of different places, and the behavior will be unexpected for some cases.

Can you apply this when setting the nickname for a contact, instead?

[pastly]

Yes. So back to silently truncating, but at 80 characters instead and additonally trimming and replacing repeated whitespaces with single spaces?

[special]

Sounds good.

Ideally, we should also change the UI where nicknames is set, to have the same maximum length and avoid confusing users too much.