Fix editing collection

[mononoken]

Currently, drop downs are generated for every journal in the collection. There should only be a drop down for adding a new journal to the collection.

Further, there should be a button to easily get a journal to leave a collection without the user leaving.

[mononoken]

The use of #fields_for in the collection _form partial is what is causing the drop downs for each journal.

[mononoken]

Fixed this issue by creating a new @new_membership instance variable and feeding this object to #fields_for instead of it inferring from the symbol call.

However, still have some cleaning up to do. I want to complete the following:

• edit view to show a list of all already included journals
• drop down only shows valid journal options (not already included journals)
• add button to remove journals from collection:
  • This should work for both own journals and other user journals (if the user is the owner)
• make sure same user having multiple joined journals works correctly

[mononoken]

This is tied to the idea of a user having multiple journals in a collection. Currently, that is not possible because of validations in membership.

I would like for the edit form to allow an owner, or anyone with the correct permission, to add additional journals to the collection. This might be especially useful for DMs or someone who has multiple characters in the same campaign.

[mononoken]

This is mostly fixed now.