Migrate new app settings to AppFramework

Let's migrate those two new files.
Properly catch 503 storage not available in getQuotaInfo

When doing a PROPFIND on the root and one of the mount points is not
available, the returned quota attributes will now be zero.

This fix prevents the expected exception to make the whole call fail.
On Windows platform we have no stable etag generation - yet
Make supported DBs configurable within config.php

This commit will make the supported DBs for installation configurable within config.php. By default the following databases are tested: "sqlite", "mysql", "pgsql". The reason behind this is that there might be instances where we want to prevent SQLite to be used by mistake.

To test this play around with the new configuration parameter "supportedDatabases".
code cleanup during review :+1:
Merge pull request #11786 from owncloud/MakeSupportedDBsConfigurable

Make supported DBs configurable within config.php
Merge pull request #11799 from owncloud/no-stable-etags-on-windows

On Windows platform we have no stable etag generation - yet
[tx-robot] updated from transifex
Merge pull request #11791 from owncloud/webdav-getquotainfo-503-handling

Properly catch 503 storage not available in getQuotaInfo
Merge pull request #11600 from owncloud/refactor-appsettings-to-app-framework

Migrate new app settings to AppFramework
l10n.pl now generates js files as well
Added OC.L10N namespace with translation functions

Added addTranslations and fixed de.js file

Fixed de.js to use OC.L10N.register() and use to correct expected
format.

Added JS unit tests for OC.L10N class

Include translations JS script for all apps
in case a translation javascript is not found we no longer bail out

remove translation.php
Include core translations

Moved search result type translations to search.js

Load JS translations earlier

Translations need to be loaded earlier to make sure that some JS files
like search.js get access to translations at this time.

This requires the template initialization to be moved to after session
initialization, because only after the session we have access to the
current language.
adding console command to generate javascript translation files based on existing php translation files
read server side translations from json files
update all translation files to js and json