Separate lock reason from summary

We recently adjusted to display the moderation reason of a topic directly
in the topic titlebar.  Since locking/unlocking a topic was setting both the
moderation reason and the summary duplicate content is being displayed. We
decided to split the two, showing the lock reason and leaving the summary alone
for usage as the users see fit.

This patch changes the locking forms and apis to accept the reason argument
instead of summary, and removes the code in the TopicSummary block that responds
to the lock-topic action.

Change-Id: Ic576481b1215f1ab0bd836915900a34a48f7047b
flow-hide role should not be considered for locked topics

The flow-hide role is given to everyone and isn't really relevnt
to lock/unlock which is only available to users.  Remove flow-hide
roles from the list of roles that enable actions against locked topics.

Change-Id: I48502ad97c672909793bf7e0f927ac66dc517ac5