Disallow campaigns with the same `CAMPAIGN_NO`?

[zouharvi]

Recently I made an error in not making CAMPAIGN_NO unique and it kind of merged accounts together (in a weird way). I wonder if this could be prevented by one of the following:

• Error in loading if an existing same CAMPAIGN_NO already exists (easy, non-invasive).
• Drop CAMPAIGN_NO from manifests and require that CAMPAIGN_NAME is unique (more invasive but seems more intuitive from user perspective).

Btw for CAMPAIGN_NAME I was thinking of allowing _- to make them more readable. Possibly even (space) because that's allowed in URLs and the redirects support it.

[zouharvi]

@snukky do you have thoughts on this? I'd like to go with the second options.

[zouharvi]

Related to #204.