List of server features

[Hywan]

Use the OPTIONS request to list features the server support. The preference is that 'listing features' is built in such a way that it could work regardless of the server.

This could list stuff like 'caldav scheduling', because the OPTIONS request reports 'calendar-auto-schedule'.

Just using the information from the Dav: header would be a good start, but we can expand this in the future by fetching information from specific webdav properties such as supported-calendar-component-set, supported-address-data, supported-report-set, etc.

Related to #236.

[evert]

I think it's more important to discover 'features' than it is to discover 'plugins', because the latter would require you to use existing APIs and it would work for non-sabredav servers.

You can actually find a lot of features with the OPTIONS http request.