nmbug-status: Slug the title when using it as an id

nmbug-status: Slug the title when using it as an id

Also allow manual id overrides from the JSON config.  Sluggin avoids
errors like:

   Bad value '#Possible bugs' for attribute href on element a:
   Whitespace in fragment component. Use %20 in place of spaces.

from http://validator.w3.org.

I tried just quoting the titles (e.g. 'Possible%20bugs'), but that
didn't work (at least with Firefox 24.2.0).  Slugging avoids any
ambiguity over when the quotes are expanded in the client.  The specs
are unclear about quoting, saying only [1]:

  Value: Any string, with the following restrictions:

    must be at least one character long
    must not contain any space characters

[1]: http://dev.w3.org/html5/markup/global-attributes.html#common.attrs.id