Added Ofir's Calendar load test.

In order to make it work, I made the following changes:

Merged Playlist::Insert() into the create() function, now there
is only one way to create a playlist.

Renamed Show::addShow() to Show::create() to make the API like
the other classes.  It returns the created show ID now.

Renamed Show::populateShowUntilLastGeneratedDate() to Show::populateShowUntil(),
allowed it to accept a second parameter for an end date.

Renamed Show::populateShowsUntil() to Show::populateAllShowsInRange().

Added documentation to a number of functions.

utils/upgrade-sql.php

@@ -1,3 +0,0 @@
-<?php
-DROP TABLE cc_backup;
-DROP TABLE cc_trans;