Add new type of graphical assets

[avivace]

At the moment, we only have a "screenshots" field, accepting PNG, BMP and JPGs. More should be added to accomodate e.g. animated graphics representing the entry.

• screenshots
• gifs
• videos

[zlago]

how does supporting links to videos count? as in, like how itch.io lets you link to a youtube video as a trailer/gameplay video

[avivace]

how does supporting links to videos count? as in, like how itch.io lets you link to a youtube video as a trailer/gameplay video

We can support "link" for assets that are more than e.g. 5MB in size? So one could attach small videos, gifs or screenshots directly in the database, but for larger assets links can be used