[Merge] lp:~dbarth/trust-store/cleaner into lp:trust-store

[David Barth]

I updated the branch with the PurgeableStore suggestion, but got straight to calling the sqlite impl class; i would have preferred to dynamic_cast instead, but my c++11 is not so great :/
-- 
https://code.launchpad.net/~dbarth/trust-store/cleaner/+merge/299294
Your team Ubuntu Phablet Team is requested to review the proposed merge of lp:~dbarth/trust-store/cleaner into lp:trust-store.