Improve clarity and make more succinct the lock warning message

Problem/Motivation

I've demoed this module to a group of ~10 people and we agreed that the warning message could use some improvement.

How it looks now:

So we have two separate warning messages, one reads:

This content is being edited by the user cm1 and is therefore locked to prevent other users changes. This lock is in place since 3 min 24 sec.

And the other reads:

Click here to Break lock

Proposed resolution

Combine the two messages into one and change the phrasing a bit:

This content is being edited by the user cm1 and is therefore locked from editing by others. This lock is in place since 3 minutes ago. You may break the lock.

Having a single message that combines the action at the end is more succinct. This also removes the seconds granularity from the message, which is likely too verbose (seconds are still used if it's less than 1 minute).

Remaining tasks

User interface changes

API changes

Data model changes