[cleanups] Uniformisation of SQL types

We simply use TEXT and INTEGER instead of VARCHAR(X)
to make the whole SQL tables more coherent. A Facebook
identifier will then always be stored as a TEXT,
same for urls and texts in general. Only numbers such
that counts and account identifiers are stored with
INTEGER.
API changes for Facebook images

Facebook images was using an old database
architecture, that provides useless fields.
These fields were also used by the whole API,
even if they don't have real usage.

This commit removes all these old fields,
including user images, and album cover images.