Allow registering of multiple methods on each api route. Add /cloud/capabilities route.

See the api route GET /ocs/v1.php/cloud/capabilities.

Output:
```xml
<?xml version="1.0"?>
<ocs>
    <meta>
        <status>ok</status>
        <statuscode>100</statuscode>
        <message/>
    </meta>
    <data>
        <capabilities>
            <files_versions>
                <versioning>1</versioning>
            </files_versions>
            <core>
                <pollinterval>60</pollinterval>
            </core>
        </capabilities>
        <version>
            <major>4</major>
            <minor>91</minor>
            <micro>9</micro>
            <string>5.0 pre alpha</string>
            <edition></edition>
        </version>
    </data>
</ocs>
```