Fixes https://github.com/turt2live/matrix-media-repo/issues/187

Fixes https://github.com/turt2live/matrix-media-repo/issues/170

There's some other functions which still need some work in order to fully complete the upload process

Another step forwards to having different storage backends. s3 uploads currently not implemented

Fixes https://github.com/turt2live/matrix-media-repo/issues/130

Fixes https://github.com/turt2live/matrix-media-repo/issues/131

Part of https://github.com/turt2live/matrix-media-repo/issues/65

Fixes https://github.com/turt2live/matrix-media-repo/issues/122

The original error was a corrupted file served over federation to us which caused format exceptions.

**Caution**: This is a major migration that changes how files are tracked within the database. Although tested to ensure things won't go wrong, there is the possibility of something going haywire. It is recommended to run the following database commands before upgrading:

CREATE TABLE media_backup AS TABLE media;
CREATE TABLE thumbnails_backup AS TABLE thumbnails;

In the event you need to roll back, run the following:
DROP TABLE media;
DROP TABLE thumbnails;
CREATE TABLE media AS TABLE media_backup;
CREATE TABLE thumbnails AS TABLE thumbnails_backup;
DELETE FROM gomigrate WHERE migration_id = 7;

This will cause any files uploaded between upgrading and rolling back to be lost.

NOTE: The migration will take a while and runs on the first access of a file. If you have a lot of files, this could take a while.

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Fixes https://github.com/turt2live/matrix-media-repo/issues/106
Step towards https://github.com/turt2live/matrix-media-repo/issues/47

Part of #58

Part of #58

The middle layer is being completely replaced. We're keeping it for reference for now though.

Part of #58

Fixes #32

This includes some refactoring to reduce the size of each file. The base cache operations (create, etc) are now in their own file for instance. The methods pertaining to just media or just thumbnails are also isolated.

They can be very CPU intensive, and people may not want to suffer that. Having the option to turn them off isn't a bad idea.

Fixes #37

* Use a swap image for resizing the frame (otherwise the frame gets corrupted)
* Use a linear resample filter (better output quality)
* Redraw the frame using a different technique
* Set the bounds of the image on the image config prior to re-encoding (otherwise the image has a bunch of whitespace)

This finishes #28

This doesn't work on two grounds:
* There is significant pixelation
* The resulting image size is wrong (but the frames are correct)

This is part of #28 and needs some cleaning up before it's an active code path. Pushing now because this code path won't be activated under normal circumstances.

This is the first part of #28. It defaults to false to maintain synapse parity and normal expected behaviour. This commit does the basic gif->png thumbnailing (forced when required), but does not handle resizing gifs.

This will make more sense when the resource locks come into play - they'll need a place to live.