Manage connection string using type converter

[glopesdev]

This PR refactors the management of connection strings in the editor using a type converter instead of a custom type. All functionality should be preserved, except that all connection string property types are now string.

This has the advantage of making operator properties more compatible when computing connection strings dynamically (e.g. loading from a file, etc).

The sub-properties Host and Port were also fused into a more general Address property, since there is a wider family of weirdly formatted connection strings which are possible in ZMQ that do not conform to the basic pattern hostname:port (see example section in zmq_pgm docs).

[glopesdev]

Two other points for consideration:

1. Most socket types provide a default action paired with their natural complementary socket (e.g. Bind for Publisher and Connect for Subscriber). This means most of the time connection strings can ignore the bind/connect character and simply use the raw protocol://address string.
2. The connection string can actually be used to specify multiple endpoints, with each endpoint separated by a comma. This is arguably more rare, but should probably be considered when using the type converter, so it does not parse away the second connection by mistake.

Given 1. and 2. it might also not be unreasonable to just provide the default connection string with no type converter and explain the syntax of connection strings in documentation.