Added slider block view for listingblock.

no longer :construction:
##### todo
 - [x] Only register view if ftw.contentpage is installed
 - [x] Make settings (auto-slide, slide-speed, effect, usw...) configureable in ListingBlock
 - [x] Update styling
 - [x] Update readme; add description how this works with ftw.contentpage
 - [x] Remove debugging stuff from buildout configuration (`development.cfg` and `sources.cfg`)