Synchronize capability for client/server layout with the server

[NiklasRentzCAU]

Continuing #195: When the client requests a diagram, it should only ask the server to do server layout if it is capable to do so. Currently there is a preference to switch between client- and server-only layout (see #195), but a better way would be to synchronize the server capabilities first in its initial LSP messaging:

1. If the server does not support server layout (serverlayout = false in init message), always do client layout.
2. If the server does support server layout, let the option decide if client- or server-layout should be used. Default should be server-layout.