Allow archiving of campaigns

[omnicolor]

Users should be able to archive (soft delete) campaigns when they've ended.

• Add affordance on the campaign's page to archive the campaign. This might be in a shared hamburger with an edit affordance.
• After archiving, the campaign will no longer show up in the campaigns list on the dashboard.
• If the user has one or more archived campaigns, add a checkbox or button next to the campaigns heading on the dashboard to show archived campaigns.

I'm not sure if it would be better to hide the archived campaigns, or sort them to the bottom of the list and de-emphasize them.

[developerluanramos]

@omnicolor
I am geting start this one. Could you assign this task to me?