[rss] Small fixes

- White foreground text now works
- Feed list title filtering is now case-insensitive
[rss/clock] Add time format and time zone config options

The clock module can now set global config options for time format and
time zone. The time command will look for user or channel preferences
first, and then for these config options.

The RSS module now reads time format from the same place: it will look
for a channel preference, then for the config option.
Merge pull request #400 from saltire/rss

[rss/clock] Add time format and time zone config options; take RSS time format from preferences
fix to duplicate column name: tz bug

Willie fails to load remind.py module due to repeat attempt to add column ['tz'] to preferences table in the setup function.

    Error in remind setup procedure: duplicate column name: tz
    (db.py:669)

Changing second add_column to ['time_format'] at line 56 fixes the bug and appears to be the intended behavior.
Merge pull request #405 from qubitsu/patch-1

[remind] fix to duplicate column name: tz bug