Time how long search requests take.

This is to help diagnose #1473.
Refactored a bit of the logging stuff in to class specific for doing it.
Passing in scope variable.

Without this, a 'loadexception' event was inadvertantly being fired even on successful search requests.
Wording change to more closely match HTTP vocab.
Refactor based on review comments.
Merge pull request #1493 from aodn/issue_1473

Issue 1473