plugins/rink: Let the user disable rink connecting to the internet

[Sntx626]

This PR adds configuration to the rink plugins so that users can disable pulling current currency conversion upon plugin startup.

This stops the rink plugin from connecting to the internet upon startup, as a result the plugin initializes much faster.

A downside is that rink no longer offers currency conversions.

The feature is opt-in, nothing should change as long as the user doesn't specifically disable the pulling of currencies for rink.

[sdaqo]

I do not know if this fits in the context of this PR, but how about caching the json file? I know currency conversion changes over time but having it cached for a day or two is probably no big deal and would also speed up init + you do not loose currency conversion. I may open another PR if this ever gets merged...