* replace line breaks (on non empty lines) in the app description by spaces
* fixes #13315
* includes unit tests

The update routine tries to test the database migration before actually performing the update.

However, this will fail hard if the schema has changed (for example an unique key has been added). App developers can convert the DB in preupdate.php, however it is not called before and therefore the update fails.

This actually breaks ownCloud updates from ownCloud 6 to ownCloud 7 when the files_antivirus app is enabled.

The script required by require_once might use variable names like $app
which will conflict with the code that follows.

This fix encapsulates require_once into its own function to avoid such
issues.

This function might also be called before ownCloud is setup which results in a PHP fatal error. We therefore should gracefully catch errors in there.

filter installed and not-installed apps properly

kill unneeded file

load category 'Installed' on page load

adding documentation links

new apps mgmt: first style adjustment

apps mgmt: only show license and preview if they exist

adding buttons

new apps mgmt: fix for mobile

use app icon if available

new apps mgmt: position enable/disable toggle to the right

new apps mgmt: proper display of icons or previews

new apps mgmt: fix loading spinner

reenable group selection for apps

new apps mgmt: position enable button normally again

new apps mgmt: clarify wording from 'Installed' to 'Enabled'

reintroduce enable/disable

Move rating image path generation to client-side

Move expression outside of l10n

fix group handling

add buttons for 'More apps' and 'Add your app' again

disable changed date of app for now

adding recommended label

style 'Recommended' app tag

fixing php warning

sort by rating

adding meta-category 'Recommended'

 Only show existing documentation links

lacy loading of screenshots

making group based app activation work again

adding support to get the app icon not only by the app name but also simply by the fixed name 'app.svg'

adding app.svg for all core apps

query string '?installed' is not longer needed

update and uninstall is back + error feedback

remove unneeded parameter

fix alignment of 'recommended' label

This allows to have links to different doc base URLs

a.

Since getEnabledApps() depends on an authentication app to be loaded,
especially in the case of LDAP, the cache from getEnabledApps() is now
cleared to make sure that subsequent calls will properly return apps
that were enabled for groups.
This is because getEnabledApps() uses the inGroups() function from the
group manager provided by LDAP or any other authentication app.

Fix issue where the currently logged user was causing side-effects when
upgrading.
Now setting incognito mode (no user) on update to make sure the whole
apps list is taken into account with getEnabledApps() or isEnabled().

Properly initialize $apps array

When upgrade, also simulate the database schema update for apps before
doing the actual upgrade.