Installer improvements

Fixes #36 and #37 

This pull request decouples various updates and installation features from `Battlelogium.Installer`, as well as adding many more features. This allows for the installer to be updated through the Battlelog client, previously the installer was the only way possible to update any component of Battlelogium and thus made the installer effectively un-updateable. Uninstallation through the Control Panel is now possible. Battlelog Web Plugins are no longer updated through the installer as they are now updated through the Battlelog client itself. The Install process is simply a wrapper over a simple updater class which extends from a reusable downloader class and adds zip file extraction to update.