Add link to prefix type help

The prefix type attribute is described in a help box but was only linked
from the add pool page. This changes so that the same link is available
on the prefix add and edit page.

Fixes #358
Raise max results for vrf listing

Tab completion for vrf listings were limited by the default max_result
of 50. The max_result is now set to 100000 for these queries and so
we've probably avoided the issue for the time being.. not sure what
would be the optimal solution. Tab completion does give much room for
things like error/warning messages and so just raising the limit feels
like the best solution for the time being. Few should need to go above
100000. Listing 10k VRFs takes about a second on my laptop..

Fixes #353.
Merge branch '353-vrf-tab-completion'
Merge branch '358-www-prefix-type-help'