POST_block: Do not check inbox if user is a mod of the subreddit.
Show only one entry per app on /prefs/apps

This changes /prefs/apps to show one entry per OAuth2Client,
with a combined scope showing the cumulative scope of all
tokens granted to the app.

Previously, /prefs/apps had one entry per access or refresh
token. This was generally redundant, as the revoke action
would revoke all tokens for the given app.
Be more explicity with merged OAuth2Scopes

In order to present a precise picture of an OAuth2Client's
overall permissions, a dictionary of OAuth2Scopes with
the exact, per-subreddit scopes is passed.
Clean up /prefs/apps view of OAuth2Scopes

Re-styles the /prefs/apps view of app permissions
so that the new, longer lists of scopes won't overflow.