[Feature request] Add maintenance hooks

[aledeg]

I think it could be useful to introduce new hooks for the extension system.
I am thinking hooks that can be use for maintenance purposes. It could be at the system level (perform a vacuum on sqlite databases), at the user level (remove useless configuration), or at the feed level (modify existing article content).

At the moment, we have the feed_before_insert hook which could be used for the feed level but it is triggered (as far as I understand) only when the feed is updated.
We also have the freshrss_init hook which could be used for the system level but it is trigger for every calls. It's probably too much for a maintenance task.

What I envisioned is hooks that are triggered only during the actualize_script.php process. In the file itself, we could have the hook at the system level and the hook at the user level. The hook at the feed level would have to be in the feedController.php process.

I suggest the following names:

• freshrss_system_maintenance
• freshrss_user_maintenance
• freshrss_feed_maintenance

[Alkarex]

Sounds good!

[aledeg]

Well, the user hook was straightforward to write.
But I don't know how the system hook could work. I've tried a few different things without success.
For the feed hook, I am reconsidering it since the feed_before_actualize could almost fulfill the same role.