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`)
PEP8!
```
extender.py:13:1: E302 expected 2 blank lines, found 1
extender.py:15:5: E301 expected 1 blank line, found 0
extender.py:17:5: E301 expected 1 blank line, found 0
extender.py:21:68: E225 missing whitespace around operator
extender.py:44:80: E501 line too long (81 > 79 characters)
extender.py:46:80: E501 line too long (316 > 79 characters)
extender.py:48:5: E122 continuation line missing indentation or outdented
```