Fix problems referencing partial 'global/nav' from layout

[timshadel]

Layout didn't get the app id appended to it, so referencing a partial with a name 'global/nav' resulted in the monkeypatching expecting that the app id was 'global'. Additionally, even if the monkeypatched vesion received a valid raw path, the raw version was never attempted.

This is fixed in two ways:

• First, we add the app id to the layout sent to any 'render' call except for layout: false
• Second, we add a fallback to the monkeypatching where we simply try what express would do with the raw path parameter

The tests show both problems.

Of note is the fact that the problem can be fixed by #2 alone, but then it always checks the filesystem twice. The change for #1 avoids that.

[timshadel]

See comments on zappajs/zappajs#8 (needs tests + doc). Closing since I won't get around to that work.