Introduce generic signature for blob files

[wipe2238]

Basically, making a feature out of #1 requirements.

blob_signature[6] = prefix (2 bytes), type (1 byte), version (2 bytes), suffix (1 byte)

Prefix

We claim FO as prefix, currently used for clientsave, simply because it's best looking one.

Type

Defines what kind of blob we're dealing with.

• Server-side
  • [x] C .client
  • [x] M .fomapb
  • [x] P .foprof
  • [x] S .fosb
  • [x] W .fo
• Client-side
  • [ ] c .cache

Version

Simple uint16 with version number. Using uint is simply overkill.

Suffix

0x00

[wipe2238]

Implemented. Cache has been left in original state, as it collides with further plans.