mod_cron: Add a 'weekly' job frequency

mod_cron: Initialize timestamp of new tasks to start of period Makes it more generic so new periods (e.g. weekly etc) can be added easily.

mod_cron: Follow convention of imports at the top

mod_http_file_share: Keep track of total storage use across restarts The value needs to be known in order to determine if additional uploads can be accepted.

mod_http_file_share: Fix measuring total storage use before it was known Passing nil to the metrics system causes errors later.

mod_smacks: Refactor, simplify, optimize Since reply.attr.to will be the .attr.from of the input we can check this earlier and avoid constructing the reply at all.

mod_smacks: Use function to construct error reply Did error_reply() not exist when mod_smacks was first created?

mod_cron: Initialize daily tasks so they run around midnight UTC Eventually the goal is to have daily tasks run while there is little activity, but that will vary with the server and the usage patterns of its users. This is a start anyway.

mod_http_file_share: Keep global storage use accurate longer. Merging those loops removes the miscounting that would occur in case a file could not be deleted, so no need to limit it to that case.

mod_http_file_share: Merge file expiry loops Not sure what the benefit of two separate loops was, perhaps reduced memory usage by allowing archive query state to be garbage collected before moving on to deleting files. Never measured so probably not so. This simplifies a bit.