fix: rightshelper: return always true when user is admin
fix: use number_field when appropriate
several enhancements for close votes
modifications on hash attributes aren't detected by ActiveRecord

In fact, all "in-place" modifications aren't detected; thus we mark the
attribute manually as dirty
DRY: split up get_thread_w_post to get_thread and get_thread_w_post
use get_thread and get_thread_w_post instead of repeating code
fixup: 39fdef0 modifications on hash attributes aren't detected by ActiveRecord
DRY: use a helper on CfMessage to determine if a message is open for answers
fix: ensure that edit/create/new for messages are only allowed when message is open for answering
fix: now using to distinct flags for NA via vote and set by admins
fix: explicitely safe the "opened by admin" flag
a lot of work on open/close votes

This should fix #94, #95