Allow placing images on top of captured territories

[cbrwizard]

Need to properly investigate whether it is needed for a project, because that's a lot of work here.

A current theory is that it's needed for the companies to properly get interested in this game as a platform.

• [x] Allow uploading images
• [x] Place an image on top of the whole player's territory

[cbrwizard]

If audience shows their interest in this https://github.com/cbrwizard/squardak/issues/117, I need to implement it quickly and unpolished to cheaply test my idea. That means, to execute it in a single next sprint and after that ask players again.

[cbrwizard]

An idea: that image should basically act like a sprite for each square object.

First of all, to determine the image size, a rectangular is drawn over the whole user's territory so that every square is inside of it. That rectangular basically has the same size the image should have. Next, an image is resized(or its resize ratio is stored) and every square now uses that image as a sprite in its background, taking the width, height, x and y.

When we upload the image, we should create and store 3 copies: small, medium and big sizes and download the needed ones.

When the player is in the login screen, the images should start downloading already.

[cbrwizard]

All right, looks like Google's Cloud Vision API is the only service I've found with both nudity and violence filters, so let's invest into that. https://cloud.google.com/blog/big-data/2016/08/filtering-inappropriate-content-with-the-cloud-vision-api

[cbrwizard]

On the other hand, let's work on censorship later, when it's needed.

[cbrwizard]

Done!