API changes for spike

These are the changes for the following tasks:

https://dev.sourcefabric.org/browse/SD-1005
Change schema to add a new attribute for spike

https://dev.sourcefabric.org/browse/SD-1010
Change desk schema to add new attribute for spike lifespan

https://dev.sourcefabric.org/browse/SD-1012
Create a global attribute for lifespan of spiked items

https://dev.sourcefabric.org/browse/SD-1013
API: Create a new end point to get archive items having spike = true

Thanks Adrian, doing a clean up now...