[2pt, 1.5pt] Revise mapping between REST/mdp URIs and majordomo messages, and subscription handling

[frankosterfeld]

Currently there are inconsistencies in how REST and mdp/mds URLs are mapped to majordomo messages and how service names and queries are supposed to look like (see also #331).

We discussed that

• service names must always start with a slash and can have sub paths. (valid: /GnuRadio/Acquisition, /dashboards/dashboard1; invalid: dashboards)
• The "endpoint" frame contains only the query part "?foo&bar" (TBD: with or without leading ?? for now, probably with, to make it work with our URI implementation)
• For subscriptions, subpaths/topics are not supported, only query parameters can be used to filter (Invalid for subscription "/dashboards/dashboard1")
• For ZMQ PUB/SUB, /serviceName?query will be used, with sorted params (as ZMQ does string matching)

Examples: (mds/mdp follows the same scheme as REST and is thus omitted)

Subscription to http://localhost:8080/GnuRadio/Acquisition?signal=test&acquisitionMode=streaming

• serviceName is /GnuRadio/Acquisition
• endpoint is ?signal=test&acquisitionMode=streaming (arbitrary param order)
• ZMQ PUB/SUB subscription string is /GnuRadio/Acquisition?acquisitionMode=streaming&signal=test(sorted params)

GET/SET to http://localhost:8080/dashboards/dashboard1

• serviceName is /dashboards/dashboard1
• endpoint is "" (empty string)
• The broker's service name matching is used so that /dasboards/dashboard1 reaches the /dashboards worker (which then parses the "dashboard1" from the service Name)

Ensure that

• The implementation of subscription, GET/SET, REST, mdp/mds clients, Workers and Broker follows the above description
• All unit tests in opencmw-cpp and usages in opendigitizer (unit tests and UI) reflect the intended behavior described above and work
• Document the intended behavior and give examples in the README