Remove /:organization_id/memberships path

[begedin]

As discussed in #341, it's not used at all.

I would like to look at other things here as well. We have tests for filtering by role level and organization id that are written as if they need to come in specific combinations. Migth be simpler to just loosen them up and simply apply supported filters "in order".

[joshsmith]

@begedin so not ready for review yet?

[begedin]

@joshsmith I removed everything that's unused by ember in a separate commit, so we can roll it back if you don't feel comfortable doing this. However, here's how our org memebrship mirage config looks like:

/**
* Organization memberships
*/

// GET /organization-memberships
this.get('/organization-memberships', { coalesce: true });

// POST /organization-memberships
this.post('/organization-memberships');

// GET /organization-memberships/:id
this.get('/organization-memberships/:id');

// PATCH /organization-memberships/:id
this.patch('/organization-memberships/:id');

// DELETE /organization-memberships/:id
this.delete('/organization-memberships/:id');

We do not have any requirements for filtering, ember side.

When we retrieve an organization, it will provide us a list of membership ids. These ids will then be fetched using coalesced requests.

An average organization will not have members numbering to a point where it would be a problem to get them all and then sort/filter client-side. If we do need additional filters, we can add them later.

If anything, what we should consider is preventing an unfiltered index-request (without a list of ids), or at least paginate or limit that response, or something.

[coveralls]

Coverage increased (+0.1%) to 95.263% when pulling 5eb783e on 341-get-rid-of-organization/memberships_endpoint into 593f659 on develop.

[coveralls]

Coverage decreased (-0.04%) to 95.088% when pulling f7fd48d on 341-get-rid-of-organization/memberships_endpoint into b0557dd on develop.