Poem security

Branched from passport-authentication

It should be possible to merge this branch in before or after the add-poem-lines (https://github.com/jimguys/poemlab/pull/15). The intention is for these two branches to be independent of each other. It might make sense to do this feature after https://github.com/jimguys/poemlab/pull/15, so we can access all poems for testing purposes.

This feature limits the poem list to only show the poems that the user has access, through the poet_poems association. When a poem is created, the poem is associated with the user that created it. 

Effectively, this limits the poem list to only show the poems that the user created, since we do not yet have a mechanism to add poets to a poem. We can either do that on this branch, or we can merge this in and do that as a separate feature branch.