Improved aliasing and plugin replacement

[bennothommo]

Combines the following PRs for better testing:

• Namespace alias support in extendable trait #27 - Namespace alias support in extendable trait
• Add reverse aliases for lazy-loaded classes. #31 - Add reverse aliases for lazy-loaded classes

[mjauvin]

I've tested the following:

• instanceof works for classes of replaced plugins.
  e.g. This works if Winter\Blog is installed and replaces RainLab\Blog:

   $model = new \Winter\Blog\Models\Post;
   $model instanceof RainLab\Blog\Models\Post; // returns true

• public $implement = []; // works for classes of a replaced plugin.
  e.g. This works if Winter\Translate is installed and replaces RainLab\Translate:

use Model;

class myClass extends Model
{
    public $implement = ['@RainLab.Translate.Behaviors.TranslatableModel'];
}

[LukeTowers]

Were we able to do any performance testing on this @mjauvin or @jaxwilko? This is such a low level feature that I want to make sure it's rock solid

[bennothommo]

@mjauvin one extra thing to test is what happens if both RainLab.Blog and Winter.Blog are installed - do the replacements work correctly, or is still a requirement to remove the original plugins first? In my testing, it seemed to be fine with both plugins installed, but just wanted to see if someone else can confirm the same.

[mjauvin]

@bennothommo I tested with both Winter/RainLab Blog plugin installed and it's working fine. @jaxwilko's code still detects and warns that both plugins are installed, but the replacement seems to not care for the replaced plugin.

[jaxwilko]

@mjauvin @bennothommo Last I left it, the desired functionality is that Winter.Blog would replace Rainlab.Blog by disabling Rainlab.Blog and showing a warning suggesting it's removal. This way the Rainlab.Blog plugin will stay in place but wont be registered and no code within it will be executed.

[mjauvin]

So, yeah, this code is what makes this work now in Support/ClassLoader::load():

        // If the class is already aliased, skip loading.
        if (in_array($class, $this->loadedAliases) || in_array($class, $this->reversedClasses)) {
            return true;
        }

[RomainMazB]

Just a little comment.