Eager bootstrapping of the plugin

[roborourke]

We can't know for sure how the plugin is loaded, eg. as a muplugin or otherwise but we can at least bootstrap it as soon as the file is loaded. This means any plugins such as Jetpack doing odd things on plugins loaded like scheduling events will be using Cavalcade instead of the options table.

Fixes #83 kind of

[rmccue]

Looking at what bootstrap() does:

• Register cache groups - should be OK, as I'm 99% certain Altis bootstraps the object cache first, and it's unlikely anyone else is doing anything as weird as we are.
• Creating DB tables - ditto above, DB almost certainly is loaded by now
• Populating the site options - this makes me a little anxious tbh, in particular the call to get_option( 'cavalcade_db_version' ) - but, that said, this may also be broken right now in multisite?
• Adding a bunch of actions - totally safe

The site option is the only one that seems maybe a bit 😬; can we at least move the get_option call into the anonymous function? Unless there was a reason that it's not... and this is also only called on single site -> multisite conversion...

[roborourke]

Completely missed that get_option() issue - yeah I'll dig into that a bit more, feels like that should just use get_site_option()

[roborourke]

@rmccue get_option() can safely be moved inside that filter, the function that calls (same name) also calls get_option() a bunch of times and there's no switch_to_blog() calls or anything like that going on.