add org.update endpoint

[nikosrossolatos]

Fixes #73

checkOrgExists

Since no org.getInfo endpoint existed, instead of creatin it i added an extra service checkOrgExists as a named export. It might be likely that we need a getOrgInfo in the future, but creating it just to use the service in this case seemed kind of an overkill.

I also thought about using the isUserAuthorised function to bail early if the user has no yeep.org.write permissions for the provided org id and then check the existance of the given org inside the service, but this wasn't so clean and it would be harder to test.

Please advise if you would prefer a different method.

OrgMemberships

Since the orgMemberships model only uses id references i didn't make any changes there.

Edit: Bear in mind that i didn't remove the '/v1/' from the docs for this endpoint. We need to make a good passthrough to all of them and i didn't want this file to miss out 🗡

Edit2: I added the extra unauthorisedOrg inside the beforeAll loop. This would be better off inside the only test that is using it, but if the test fails before the org is deleted, then the database needs reset. It is ugly but it was worse if i left it inside the unit test.

[nikosrossolatos]

@jmike if we don't proceed with the extra validation checks because of the circular dependancy above then this PR is ready to be merged