Message.toString() should include the flag

[acasteigts]

The current version of Message.toString() shows only the content of the message, not its flag, which should be added.

[acasteigts]

What's been done in branch feature/105-message-to-string-flag:

• The Flag is now present in the String representation of a Message
• The nodes IDs are used in this representation

Merged into develop.

[acasteigts]

(Will be closed when released.)

[acasteigts]

After discussions:

• The use of Node.toString() in Message.toString() was restored, instead of Node.getID().
• The inclusion of the flag is still added.

[remikey]

@acasteigts, I took the liberty to slightly modify your Changelog commit to try and minimize discrepancies with the rest of the file.

Otherwise, ok for me.

[remikey]

merged into develop.