Added some properties to projects

[gbeine]

I've added some additional properties to projects.
I use these properties according to the description.
Merge it, if you like - and thanks for the schema :-)

[stp-ip]

In my personal opinion I see the value of those, but they don't map well to the general projects. As the schema allows for optional fields, these might be better kept optional, but happy for others to voice their opinions. If you think they could be made more general, while still being helpful, happy to discuss :)

[gbeine]

@stp-ip - thanks for the feedback!
I'll make these fields optional.
Thought, I did this, but obviously, I'm wrong ;-(

[stp-ip]

Clarification. I meant optional in terms of addition to each personal schema and most likely not something general enough to be included into the schema, but as I said happy to hear from others as well :)

[shamoons]

I think the fields, even optional, don't extend to multiple use cases.