Webform contextual links are shown to users who don't have access to them, and code can be simplified

In #1336994: Contextual links for Webform Blocks and Nodes, webform-related contextual links were added to the module. However, I'm running into a problem with this because the links are displaying even to users who do not have permission to visit the "Webform" or "Results" pages (so that when they click on the corresponding contextual link they get taken to an access denied page).

The attached patch fixes this by using hook_menu() to define the contextual links, which also simplifies the required code a fair amount.

A side effect (new behavior) of this patch is that on webform blocks, the standard node-related contextual links (e.g. "Edit" and "Delete") are also going to start appearing, in addition to the "Webform" and "Results" links. I think that's probably OK; the webform node is being displayed in the block in a teaser-like format, so it probably makes sense to show all the contextual links that would normally be attached there. If we want to hide "Edit" and/or "Delete" instead, though, it's pretty easy to do that in hook_contextual_links_view_alter(). I actually have some code in the Media Gallery module that more or less does the same thing and which could be ported here if necessary.