add phpdoc

It's only reasonable to have proper type hinting here which might even help us to catch bugs.

There is not much sense in having these files marked executable, we should avoid that.

FIXME: Ugly hack to prevent SVG of being returned if the SVG
provider is not enabled.
This is required because the preview system is designed in a
bad way and relies on opt-in with asterisks (i.e. image/*)
which will lead to the fact that a SVG will also match the image
provider.

Conflicts:
	lib/private/preview.php

The "*/*" provider has been removed. This is therefore not needed anymore and leads to unexpected bugs.

Please notice that this is only relevant for master.

a

This function is also used in a way such as:

```
	$preview = new \OC\Preview(\OC_User::getUser(), 'files');
	$info = \OC\Files\Filesystem::getFileInfo($file);
	if (!$always and !$preview->isAvailable($info)) {
		\OC_Response::setStatus(404);
	} else {
		$preview->setFile($file);
		$preview->setMaxX($maxX);
		$preview->setMaxY($maxY);
		$preview->setScalingUp($scalingUp);
		$preview->setKeepAspect($keepAspect);
	}
```

Which won't work anymore since `setFile` is used instead of passing the file in the constructor. Fixes a regression in master.

Thumbnail generation

Removed Log

Added requested changes

Added requested changes.

- Fix code style
- Add exception if file does not exist
- Switch route styling

Replaces https://github.com/owncloud/core/pull/10805

Fix codestyle

Fix codestyle

Migrate to appframework

Fix typo

Fix #9968

* test case added to avoid adding them later

Images on public sharing get downscaled to increase use experience - this will speed up loading time

- adding keep aspect to core/ajax/preview.php
- remove duplicate method Preview::show()
- no more hard coded mimetype of preview
- remove .png from the preview urls
- keep old route preview.png for backwards compatibility
- aspect preserving previews are now cached