feat(sequence): support re-rendering. closes #33.

Parsing the sequence is done in three stage: mix -> inherit -> interpolate.
This advances issues #7 and #29.
feat(piPage): should remix questions after each change. closes #29
bug(questController): results where not being saved when questions where re-rendered
feat(piqPage): throw a warning when a question name is reused. Closes #32.
feat(questController): Each question should have serial number. Closes #30
chore(questController): move decline code into the question controller.
feat(piPage): Log submit time. Closes #31