* interfaces for the Admin settings (IAdmin) and section (ISection)
* SettingsManager service
* example setup with LDAP app

Class Throttler implements the bruteforce protection for security actions in
Nextcloud.

It is working by logging invalid login attempts to the database and slowing
down all login attempts from the same subnet. The max delay is 30 seconds and
the starting delay are 200 milliseconds. (after the first failed login)

Added systemtag to group mapping table.
Added methods in ISystemTagManager to get/set the group mappings.

add some range to time() assertions

add token type column and delete only temporary tokens in the background job

debounce token updates; fix wrong class import

* Update last_activity timestamp of the session token
* Check user backend credentials once in 5 minutes

add 'last_activity' column to session tokens and delete old ones via a background job

* Add InvalidTokenException
* add DefaultTokenMapper and use it to check if a auth token exists
* create new token for the browser session if none exists
hash stored token; save user agent
* encrypt login password when creating the token

* Add extra db column to filecache
* Bump version
* Update filecache code to actually handle checksum
* Webdav code to store/retrieve checksums

CredentialsManager performs a simple role, of storing and retrieving
encrypted credentials from the database. Credentials are stored by user
ID (which may be null) and credentials identifier. Credentials
themselves may be of any type that can be JSON encoded.

The rationale behind this is to avoid further (mis)use of
oc_preferences, which was being used for all manner of data not related
to user preferences.

Added SystemTagManager and SystemTagObjectMapper

We need to store the owner of a file in the db to do efficient queries
on the owner of a file. Without this we need to construct fill paths for
each file id in the table and see who the owner of a file is. Which does
not scale.

* used only for windows support
* windows support was dropped in 8.2.0 - see #17379
* was introduced in fd8cb997
* ref #18935

Storage status is saved in the database. Failed storages are rechecked every
10 minutes, while working storages are rechecked every request.

Using the files_external app will recheck all external storages when the
settings page is viewed, or whenever an external storage is saved.

* causes issues on InnoDB because it exceeds the maximal key length
  of an index which is 767 (3-byte charset * varchar(512) = 1536)
* fixes #17619

* file_target is often used in the sharing code in JOIN statements for retrieval of shares

This reverts commit c9b56084.

This reverts commit f6a452ca.