Initial code to track post reactions elsewhere.

Very initial code, just checking how it might work.
Merge branch 'master' into reactions
Reactions() class additions. Now partly works.
post URL is stored in temporary DB.

The post URL was part of the "meta" data that were originally
stored as a serialized object in the DB filed "meta".

In order to be able to query the DB using the URL (required
to handle reactions), URL is also stored in a separate DB col.
Reactions updates.

- bucket3 has new option "reactions".
- conf.example.yaml placeholders for twitter credentials, removed
hardcoded credentials from reactions.py.
- getTwitterReactions() will touch the coresponding (to the URL)
post file, so it will be re-rendered next time "bucket3 update"
is run.
Reactions data are passed to post.html remplate
twitter user name and screen name bug fix.
Added Reactions.hash() method to abstract hashing method.
Twitter avatar caching and bug fixes
CSS and template mods to support "reactions".

Modified default CSS, and templates (base.html, post.html)
to support "reactions".
Minor text edit.