Refactor web filters and servlets to make transport more pluggable

A few of the filters and servlets have extra logic that would likely need
to be reused in other transports - especially MINA.

It would be nice if the servlets and filters were limited to reading of
request parameters and outputting of errors. The real work would then be
reusable by other transports as well as make it easier to write custom
transports.

Also, remove the filters from the web.xml to the symmetric config. This allows
for easier configuration as well as more complicated filtering patterns.
In addition, its easier to disable filters and configure them since the
properties can now be strongly typed instead of parsed in the
Filter.init(FilterConfig) method.