[WIP] Update Manager Refactor

[jaxwilko]

Me and Luke are working on a little refactor of how the UpdateManager works...

It also includes some components from my old composer PR found here: #967

The core idea of this is that there should be consistent interfaces to interact with different things built on top of Winter (i.e. modules, plugins & themes). Each of these elements will now have their class (i.e. Theme, PluginBase, ModuleServiceProvider) will now extend WinterExtension which will allow them to all interact with the update manager and other system functions directly.

In addition PluginManager, ThemeManager & ModuleManager (new) will all implement the ExtensionManager interface, which will allow for a consistant way to interact with all Winter extensions.

I.e. You will be able to call PluginManager::instance()->update($plugin) or ThemeManager::instance()->update($theme).

This also allows us to do some cool stuff like (only support for plugin installing is currently functional)

(new ExtensionSource(
    ExtensionSource::SOURCE_COMPOSER,
    ExtensionSource::TYPE_PLUGIN,
    composerPackage: 'jaxwilko/datamigrator'
))->install();

(new ExtensionSource(
    ExtensionSource::SOURCE_COMPOSER,
    ExtensionSource::TYPE_THEME,
    composerPackage: 'jaxwilko/custom-theme'
))->install();

(new ExtensionSource(
    ExtensionSource::SOURCE_LOCAL,
    ExtensionSource::TYPE_PLUGIN,
    code: 'winter.demo'
))->install();

(new ExtensionSource(
    ExtensionSource::SOURCE_LOCAL,
    ExtensionSource::TYPE_PLUGIN,
    path: 'plugins/winter/demo'
))->install();

By the end of the PR, the UpdateManager as is may no longer exist as is, instead each ExtensionManager will be responsible for it's existing functionality.