Add warning/watch/alert plugin

Add warning/watch/alert plugin

Note: this is development code and will not run without the following:

- An xml alerts file. The alerts feed [1] has some issues which need to
  be resolved before much more development is done. These include
  missing data (hazard's weather outlook), missing lat-lon polygons (for
  SVR/TOR warnings), unknown sorting order, and inconsistent use of fips
  and NWS warning area codes.

- A fips polygons file. The original was found as a link from the CAP
  cookbook/wiki [2]. However, this contained a convex hull of each
  county, which is not entirely useful. Andy Spencer created two more
  which are hopefully a little more useful but contain a larger number
  of points and require tessellation to use [3].

[1] http://www.weather.gov/alerts-beta/us.php?x=0
[2] http://www.incident.com/cap/fips_polys.txt
[3] http://andy753421.ath.cx/linked/fips_polys_{simp,full}.txt