views: support "from" parameter in addition to "page" for use with infinite scroll

[lnielsen]

Trying to implement an infinite scroll with the Invenio REST API is somewhat complicated from the fact that you need to provide page + size parameters. Would be easier if it was from and size. Also, it would be useful to be able to turn off aggregations for all but the first request (when in an infinite scroll). Via Cottage Labs

[lnielsen]

Needs a change to views:RecordsListResource.get() with something along the lines of:

size = request.values.get('size', default_results_size, type=int)
page = request.values.get('page', None, type=int)
from = request.values.get('from', None, type=int)

if from is not None and page is not None:
    abort(400, ... explain ...)

if page is not None:
    from = page * size

if from is None:
    from = 0

if from < 0:
    abort()

if size < 1:
    abort()

• from and page cannot be specified at the same time
• from >= 0, page > 0 or size > 0 must be true
• Link (prev/next/self) generation should use the same parameter as the user (i.e. either page or from)