Basic async build of course size report.

[danmarsden]

This is a basic version of an async report.

I made a few decisions here that are worth documenting.

• We only really need to make the overall stats use an async process - the queries to generate specicfic course info is pretty quick when restricting to a single course (or should be improved to be quick.)
• sites using the old async branch will need to be careful upgrading to this branch as the tables do not match.
• I decided to make it always use the cached table rather than allowing a direct query on files table and didn't add config to allow this to be turned on/off (we could look at this later, or potentially allow an ad-hoc task to be triggered to refresh it if needed.)

Still a lot of code that would be nice to clean up in this, but wanted to minimise the changes to just the stuff neccessary for async support.

[danmarsden]

Note: - I'd ideally like to fix the behat tests on the main branch before we merge this so we can see it passing in both mysql and postgres.

[danmarsden]

Now that I'm thinking about that behat test... I'm tempted to add a setting in that allows it to build the cache table on page-load if not populated recently.... easier than trying to trigger a scheduled task in behat.

[brendanheywood]

Looks great, minor comments in the pr, also make sure we close this one when we merge this:

https://github.com/catalyst/moodle-report_coursesize/issues/15

[danmarsden]

thanks Brendan - good to have someone elses eyes on this.

[brendanheywood]

@danmarsden this looks good to me, I'll let you sort behat and merge whenever

[danmarsden]

merged manually - ended up adding a live/scheduled task setting in the end so that people can still run the report directly rather than using scheduled task - it is set to run via scheduled task by default.