internal: Improve handling of taxonomy term slugification. This paves the way to bring slugification options like transliteration to PieCrust. This change mostly makes sure we use one-way slugification, which means, for serving/previewing, we need to slugify each page's terms to compare to the stuff captured from the URL. It also simplifies things a bit in the code.

cov-core==1.15.0
coverage==3.7.1
mock==1.0.1
pytest==2.7.0
pytest-cov==1.8.1
pytest-mock==0.4.3