Add failure message to requirements

[ibboard]

To make requirements more useful to the user, they need to report a failure message.

[ibboard]

In [916]:

Re #345: Add failure message to requirements

• Add abstract requirement class to handle some of the message commonality

[ibboard]

In [917]:

Re #345: Add failure message to requirements

• Implement new method from requirement interface
• Add first tests for "at least" requirement

[ibboard]

In [918]:

Re #345: Add failure message to requirements

• Implement message creation for "at least" requirement

[ibboard]

In [919/warfoundry]:

Re #345: Add failure message to requirements

• Add tests for "unit at least" requirement

[ibboard]

In [920]:

Re #345: Add failure message to requirements

• Add protected property to hold prefix for validation string, as that is all that changes

[ibboard]

In [921]:

Re #345: Add failure message to requirements

• Test return of messages from requirement handler

[ibboard]

In [922]:

Re #345: Add failure message to requirements

• Return message for each failure (don't stop at first one)

[ibboard]

In [924]:

Re #345: Add failure message to requirements

• Add tests for "no more than" requirements

[ibboard]

In [925]:

Re #345: Add failure message to requirements

• Add implementation that lists only failed parts for "no more than" requirements

[ibboard]

In [928]:

Re #345: Add failure message to requirements

• Add testing of failure messages for "allows adding"

[ibboard]

In [929]:

Fixes #345: Add failure message to requirements

• Add implementation of failure messages for "allows adding"