Make "export to .vpx" available in the editor

[freezy]

VPE can write .vpx files, but currently there is no way from the editor to actually do that.

A .vpx file consist of:

• Table Info (pre-defined and custom key/values)
• Table Data
• Other game items
• Collections
• Images
• Sounds
• Fonts
• Some meta, like hash and file format version

If we want to read and write data in a consistent way, we need Unity to serialize it so what we want to write is also available runtime and doesn't get lost during reloads.

That means our data classes need to be all [Serializable]. Before writing, we would create a new Table object based on the serialized data, and then use its API to write the .vpx. So what needs to be done:

• Store table info somewhere on a GameObject
• Create a component per game item (see flippers and table, where it's somewhat implemented)
• Store invisible components (like timers) somewhere
• Somehow store collections
• Find a way to pull the texture assets back as VPX textures
• Deal with sounds
• Deal with fonts (add read and write support already)

To be clear, this means that we create a new .vpx from scratch every time we export (as opposed to taking an existing file and only patching the differences).