[4] Fine-grained node management

Follow up from #1901

Node management

- The user should be able to define favorite nodes (that he knows are connecting fast). The ping strategy will then consider those first
- The user should be able to disable nodes (that he knows he never wants to connect to). Those nodes will then be ignored at all times
- Add a checkbox "Only connect to favorites" (accounts for @startailcoon s comment below)

Start by reading the follow-up in #1901 and tracing the existing node connection and ping strategy entry points. Confirm how nodes are currently selected, then define done as supporting favorites, disabled nodes, and an "Only connect to favorites" option without connecting to disabled nodes.

Written by the indexing model from the issue text.