Feature/new archiving (#2335)

* Change archiving config page layout

I've changed some wording and moved actions into a
maintenance section.

* Update purge action

Now we have more control on the purge action. The configuration allows
us to choose what to keep and what to discard in a more precise way.
At the moment, the configuration applies for all feeds.

* Add purge configuration on feed level

Now the extend purge configuration is available on feed level.
It is stored as attributes and will be used in the purge action.

* Update purge action

Now the purge action uses the feed configuration if it exists and
defaults on user configuration if not.

* Add empty option in period list

* Fix configuration warnings

* Add archiving configuration on categories

See #2369

* Add user info back

* Add explanations in UI

* Fixes for SQLite + error + misc.

* Fix invalid feed reference

* Short array syntax

Only for new code, so far

* Fix prefix error

* Query performance, default values

Work in progress

* Fix default values and confirm before leaving

Form cancel and confirm changes before leaving were broken.
And start taking advantage of the short echo syntax `<?= ?>` as we have
moved to PHP 5.4+

* More work

* Tuning SQL

* Fix MariaDB + performance issue

* SQL performance

* Fix SQLite bug

* Fix some attributes JSON encoding bugs

Especially for SQLite export/import

* More uniform, fix bugs

More uniform between global, category, feed settings

* Drop special cases for old articles during refresh

Instead will use lastSeen date with the new archiving logic.
This was generating problems anyway
https://github.com/FreshRSS/FreshRSS/issues/2154

* Draft drop index keep_history

Not needed anymore

* MySQL typo

Now properly tested with MySQL, PostgreSQL, SQLite

* More work for legacy values

Important to avoid overriding user's preference and risking deleting
data erroneously

* Fix PHP 7.3 / 7.4 warnings

@aledeg "Trying to use values of type null, bool, int, float or resource
as an array (such as $null["key"]) will now generate a notice. "
https://php.net/migration74.incompatible

* Reintroduce min articles and take care of legacy parameters

* A few changes forgotten

* Draft of migration + DROP of feed.keep_history

* Fix several errors

And give up using const for SQL to allow multiple database types (and we
cannot redefine a const)

* Add keep_min to categories + factorise archiving logic

* Legacy fix

* Fix bug yield from

* Minor: Use JSON_UNESCAPED_SLASHE for attributes

And make more uniform

* Fix sign and missing variable

* Fine tune the logic

1 files changed, 8 insertions, 2 deletions

diff --git a/config-user.default.php b/config-user.default.php
index 950bef045..5b49d689a 100644
--- a/config-user.default.php
+++ b/config-user.default.php
@@ -5,8 +5,14 @@
 # override.
 return array (
 	'language' => 'en',
-	'old_entries' => 3,
-	'keep_history_default' => 50,
+	'archiving' => [
+		'keep_period' => 'P3M',
+		'keep_max' => 200,
+		'keep_min' => 50,
+		'keep_favourites' => true,
+		'keep_labels' => true,
+		'keep_unreads' => false,
+	],
 	'ttl_default' => 3600,
 	'mail_login' => '',
 	'email_validation_token' => '',