Generate the device Class programmatically

[whot]

Nothing uses libwacom_get_class() (except for identifying remotes, see #779) but we still have to add it each .tablet file. Since we don't have any known callers we can just generate the value:

• IntegratedIn=Display -> Cintiq
• IntegratedIn=Display;System -> ISDV4
• IntegratedIn= -> Bamboo

[redstrate]

I started work on this, but it dawned on me that there's a lot of classes other than Cintiq, ISDV4 and Bamboo. I guess it makes sense to only generate it programmatically if it doesn't have an explicit one defined?

[whot]

The only class that currently matters is the WCLASS_REMOTE, all the others are never used for anything (afaik). Many are expired and now pointless anyway (Intuos*, Bamboo, Graphire). So the only ones that "matter" are Cintiq, Intuos5 and ISDV4 - all of which we can auto-assign.

And the remote of course :)

[whot]

Fixed in #814