Inherit Campaigns when adding Indicator via Object

When adding an Indicator by adding a new Object or clicking the "+" next to an existing object, it makes sense that the new Indicator inherit the Campaigns of the top-level object. At some point "indicator_campaign" and "indicator_campaign_confidence" were added as parameters to the add_object function, but as far as I can tell they are never used by anything and I couldn't come up with a case where they would be used, so I removed them.

This PR also:
- Fixes display of errors when "+" is clicked (which was broken at some point), and also notifies the user if an Object is added, but creation of the associated Indicator fails.
- Fixes the KeyError that would occur if a Campaign's Confidence field was blank
- Prevents assignment of a new Campaign from replacing an existing Campaign of the same name. The auto-replacment only occurred if the new Campaign had greater Confidence, but seemed unintuitive since there is already an Edit button for each Campaign. To make matters worse, the new matching Campaign was added to the Campaign list, but upon page refresh, one entry would disappear.