(Feature) Clear a modRegister.
using $register->clear($topic)
(feature) With any registerLogging request using register&topic, add a new "clear" flag to empty the register.
(bug fix)  clear the register before cache clear.
Add modRegister::clear() method

Merge remote-tracking branch 'origin/pr/565' into develop

* origin/pr/565:
  (Feature) Clear a modRegister. using $register->clear($topic)
Add clear flag to modRequest::registerLogging()

Merge remote-tracking branch 'origin/pr/566' into develop

* origin/pr/566:
  (feature) With any registerLogging request using register&topic, add a new "clear" flag to empty the register.
Clear register before calling clear cache

Merge remote-tracking branch 'origin/pr/567' into develop

* origin/pr/567:
  (bug fix)  clear the register before cache clear.