Push using presets forward. Remove default values form Posts::get(). Fixes #353

* Remove default values: <code>Posts::get()</code> now really returns all posts no matter what, how many, and not ordered when called without any parameters.
* Make it possible to build presets on top of presets
* Push presets: Make all pages that display entries rely on presets.
* New flow preset: All presets are built on top of the flow preset (except the admin one). So if for example I add a content type and want it to display everywhere where posts usually appear, I only have to add it to that preset. Done.
* Presets in admin: That was the part that took me most of the time. The Manage page now uses a preset so it also can be modified by plugins. Still, it does not work 100% as the creepy timeline crashes the party. That can not be fixed 100% as the slider has min and max width. If we would pass the limit to the Javascript, it would still propably not be realized in a good way, so I left that part out entirely. The Manage page does not always show the same number of posts anyway...