LP#1785061: move the filter value munging to the template service

LP#1785061: move the filter value munging to the template service

This allows the reporter app to stay a bit more focused on
display concerns.

Here's a test plan for the patch series
---------------------------------------
[1] Create a reporter template that has a filter field
    and a filter operator of "In list", "Not in list", "Between",
    or "Not between" and hard-code a value for that filter
    in the template, separating values with a comma.
[2] Try to create a report from that template; note that it
    fails with an error.
[3] Apply the patch and repeat steps 1 and 2. This time, the
    report should succeed.

Note that this fix applies only to hardcoding filter values in the
template; it doesn't change any behavior when attempting to set
a filter value for any of the four operators above at the point of
creating a report.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>