`auxiliary.webcontentresolver` needs a little bit of love

[cyberMilosz]

The auxiliary.webcontentresolver module mostly works, except the root page no longer lists all providers as it's supposed to.

What needs doing:

• Broken exception handler still relies on e.message(), which doesn't exist. We probably more generally want to fix up ReflectionException and make sure we have a way of extracting good messages from it.
• Root page is supposed to "show all content providers on the device as well as some information about them", but it doesn't. [EDIT: this is because of #450]
• This module is scarcely documented. Short mention in The Mobile Application Hacker's Handbook, but that's about it.
  • Should be included in the manual
  • help auxiliary.webcontentresolver should provide a little bit more of an explanation on what's going on.
  • Existing sieve exercise on SQLi should be sufficient as an example here

[cyberMilosz]

Fixed in linked branch, pending regression testing as per #450