refactor STI specs into one file

Squashed commit of the following:

commit 61552514322dbd725a34cfec62f94d2a3b72f3bb
Author: Joost Baaij <joost@spacebabies.nl>
Date:   Wed Apr 24 22:41:09 2013 +0200

    STI specs: ownership

commit d4f493ecae9a73693ee39bdbda41232bd637a793
Author: Joost Baaij <joost@spacebabies.nl>
Date:   Wed Apr 24 22:37:38 2013 +0200

    STI specs: related tags and tag list

commit dc84ec8b2c73b6e0f061ab199cb2c6460205de8c
Author: Joost Baaij <joost@spacebabies.nl>
Date:   Wed Apr 24 22:20:40 2013 +0200

    STI specs: extract matching contexts vars

commit 2095bea6f15fd775186a348c3ac20b29d3c79f5a
Author: Joost Baaij <joost@spacebabies.nl>
Date:   Wed Apr 24 22:09:32 2013 +0200

    STI specs: extract context vars

commit b02bd7e37bd153528e0fe37cc8530fb052ae192d
Author: Joost Baaij <joost@spacebabies.nl>
Date:   Wed Apr 24 22:03:32 2013 +0200

    Pull out STI specs into a separate file

    Need to investigate #220 and the specs are just a mess.