require a minimum user karma to upvote and downvote

[xrpd]

This is intended to resolve issue #550.

A new global 'no_voting_threshold' is added. A user's karma must be greater than this value before the upvote and downvote icons will appear (i.e., before thing.votable is set to true). The modification to link.py is made in the two places that also prevent an author from upvoting their own articles and comments.

I modified example.ini, test.ini and provisioning/cookbooks/lesswrong/templates/default/development.ini.erb to include a 'no_voting_threshold' example. It will have to be added to a production .ini file to successfully implement this patch.

Tested with no_voting_threshold at various values. The voting icons appear and disappear depending on user karma as expected.

[xrpd]

Agreed, and will do. I was just wary of renaming existing configuration options without encouragement.

[xrpd]

@wezm global configuration parameters renamed per your suggestion.

[wezm]

Looks good. @cdaloisio note that ini file changes will be needed before this can be deployed.

[cdaloisio]

Great :+1: Production config values are now as follows:

karma_to_vote = 10
karma_to_vote_on_polls = 0

[cdaloisio]

Closes #550