Integrate CESNET/rousette for RESTCONF support

[troglobit]

For proper RESTCONF support with sysrepo we should add https://github.com/CESNET/rousette and its companion packages. This would enable implementing a WebUI that can traverse the YANG tree and, similar to klish, create a default hierarchy of both configuration and operational state. Specialized views, composing various YANG nodes, into logical setup/wizard like configuration is also possible.

Depends on #326 since Rousette requires newer libyang + sysrepo.