Add HIDDEN/DELETED_BY/AT columns and post actions

And merge 'FlagIllegal' and 'FlagCopyVio' into 'FlagInapt'.
Remove PAP.Undo.
Load and save tree/post-deleted-by.
Add [post/tree][Deleted/Hidden]ById to ElasticSearch, index fewer fields.
Rename two functions.
Update DW1_POSTS indexes: take deletions into account.
Don't sort posts again in loadPostsRecentlyActive()

Accept the db sort order instead, sorting again can only result in bugs.
Make ClearFlags work.