Replace [Schema]/[Collection]By[Foo] funcs with filterable param

[AndrewSisley]

At the moment we have these two sets of functions on client.Store:

GetCollectionByName
GetCollectionsBySchemaRoot
GetCollectionsByVersionID
GetAllCollections

GetSchemasByName
GetSchemaByVersionID
GetSchemasByRoot
GetAllSchemas

As well as being a lot more numerous than they need to be, they are also limited in that you can't fetch by multiple params (e.g. filter by Name and Root).

We should consider replacing them with something along the lines of:

struct Filter {
  Name Option[String]
  Root Option[String]
  ID Option[String]
}
GetCollections(...CollectionFilter)
GetSchemas(...SchemaFilter)

[nasdf]

I like this simplification. I'd also suggest adding some simple helpers:

type CollectionFilterOptions {
  Name Option[String]
  Root Option[String]
  ID Option[String]
}

var CollectionFilter CollectionFilterOptions{}

func (f CollectionFilterOptions) ByName(name string) CollectionFilterOptions {
  f.Name = name
  return f
}

...

CollectionFilter.ByName("Users")