Pull request: #379 Remove #maincontent prefix

I'm going to turn this into a pull request so that I can see the merge status bar and keep it updated.

I think the impact of this will be less than I was previously thinking because we're moving rules down the stack, not up.

I believe there will be little, if any, impact on sites created wholly within the UNL template environment.

The problems are likely to come from template integrations with third party apps with CSS not written by a unl person.

Example case where there would be an issue:

Before:
````css
#maincontent a {
    color: red;  /* wdntemplates */
}
ul.vendor a {
    color: green;  /* css shipped by vendor, not really noticed because the links display red */
}
````

After:
````css
ul.vendor a {
    color: green; /* uhoh, now links on the app are green */ 
}
a {
    color: red; /* wdntemplates */
}
````